Gao Group – Case Western Reserve University

Welcome to Xuan Gao’s Group Website

Welcome to the homepage of Professor Xuan Gao’s research group at the Physics Department of Case Western Reserve University. We are a group of experimental physicists studying a wide range of interesting subjects in the fast-growing field of nanoscale physics which bridges condensed matter physics and nanotechnology. Our research is centered on nanostructures or materials (quantum wells, nanoplates, nanowires etc) in which the quantum nature of particles (electrons, phonons etc) plays a fundamental role in their electrical, thermal, optical and magnetic properties. We seek to understand and exploit the quantum physics in these nanostructures for novel device applications.

Our current research projects include:

Electron transport and phase transitions in correlated two-dimensional electron (or hole) system in semiconductor quantum wells.
Quantum confinement, spin-orbit coupling, topology/symmetry protection effects in topological states of matter (topological insulators, Dirac semi-metals etc).
Understanding the energy conversion processes in emerging materials relevant to renewable energy.
Nanowires or graphene-like atomically thin semiconductors for next-generation nanoelectronics, optoelectronics, or biosensors.

Please visit our research projects webpage for more details.

What’s New

Prof. Gao is taking a sabbatical leave at National Taiwan University as a visiting professor this Fall.
10/2020 Another publication for Arvind: “Interfacial Charge Transfer and Gate-Induced Hysteresis in Monochalcogenide InSe/GaSe Heterostructures” ACS Applied Materials & Interfaces 12 (41), 46854-46861 (2020). We also congratulate undergraduate coauthors Mingyuan, Yancheng, and Ryuji.
09/2020 Congratulations to Arvind on the publication of “Electron-electron interactions in the two-dimensional semiconductor InSe“Phys. Rev. B 102, 121301(R) (2020). Graduate student Kasun and undergraduate Min Gao were also coauthors.
08/2020 Congratulations to Kyle on the publication of “Electrical Characterization and Charge Transport in Chemically Exfoliated 2D Li_xCoO₂ Nanoflakes”, The Journal of Physical Chemistry C, 124, 38, 20693–20700 (2020).
08/2020 Brian Holler’s paper “2D Semiconductor Transistors with Van der Waals Oxide MoO₃ as Integrated High-k Gate Dielectric“, Advanced Electronic Materials, 6(10), 2000635 (2020), is accepted and published. This paper reports MoO3 as a new two-dimensional oxide dielectric with a high dielectric constant for high performance nanoelectronics and capacitors. Congrats to Brian on publishing his first paper in the group!
04/2020 Kyle Crowley defended his Ph.D. thesis online (due to the pandemic). Congratulations! Kyle will work with Dr. Ina Martin at the MORE center during the summer and then join NASA Glenn Research Center as a postdoctoral fellow.
12/2019 Clara’s invited topical review on topological nanomaterials, “Topical Review: Development of Topological Insulator and Topological Crystalline Insulator Nanostructures“, is published as Nanotechnology, 31, 192001 (2020). Congratulations.
12/2019 Our group’s paper on topological insulator nanowires is accepted as a contribution to the special issue in Nano Research honoring Prof. Charles Lieber. In this work, we discovered that the well known weak antilocalization effect evolves into a linear magneto-resistance as the Dirac point is approached by gate tuning topological insulator nanowires, giving key insight to the puzzling origin of the linear magneto-resistance effect found in various topological materials hosting Dirac carriers. This work is done in collaboration with LingNan Wei, Prof. ZhenHua Wang and Prof. ZhiDong Zhang at the Chinese Academy of Sciences. “Enhanced linear magneto-resistance near the Dirac point in topological insulator Bi₂(Te_1−xSe_x)₃ nanowires“, Nano Research, in press (2019).
12/2019 Our group published a few collaborative papers with the Chinese Academy of Sciences on topological insulator and 2D semiconductors:
- “Giant Linear Magnetoresistance and Carrier Density Tunable Transport in Topological Crystalline Insulator SnTe Thin Film” Physica Status Solidi B-Basic Solid State Physics, 256, 1900139 (2019).
- “Broadband Photodetection of GeSe Films of Vertically Grown Nanoflakes“, ACS Applied Electronic Materials, 1(11), 2236-2243 (2019).
- “From linear magnetoresistance of parabolic magnetoresistance in Cu and Cr-doped topological insulator Bi₂Se₃ films“, Jour. of Phys. and Chem. Solids, 128, 331-336 (2019).
11/2019 Kasun Premasiri defended Ph.D. thesis and will start as a postdoc fellow at Microsoft Station Q at Purdue University, working with our collaborator Prof. Michael Manfra. Congratulations and good luck, Kasun.
11/2019 Our group publishes a joint paper with Prof. Lei Zhu’s group on a new high-k polymer dielectric for nanoelectronics: “High κ Polymers of Intrinsic Microporosity: A New Class of High Temperature and Low Loss Dielectrics for Printed Electronics“, Materials Horizons, in press. Kasun is the main contributor from our group.
10/2019 Clara finishes her postdoc in the group and moves on to explore medical physics research with Dr. Ping Xia at Cleveland Clinic. Congratulations and good luck, Clara.
5/20/2019 Prof. Gao attended the annual AFOSR program review on 2D oxide project at Washington DC.
4/20/2019 Prof. Gao visited Harvard and gave a talk on nanowires with spin-orbit coupling at the CML symposium celebrating Prof. Charles (Charlie) Lieber‘s past and ongoing achievements. Happy Birthday, Charlie!
4/4/2019 Prof. Gao visited Ohio University and gave a seminar on 2D layered materials at the Nanoscale and Quantum Phenomena Institue.
3/8/2019 Prof. Gao gave an invited talk on monochalcogenides, a new family of graphene-like two-dimensional semiconductors with atomic thickness, at the annual March meeting of American Physical Society. Group members Kasun and Arvind also gave three contributed talks.
3/6/2019 Kasun’s work “Electrically Driven Structural Phase Transition in Single Ag₂Te Nanowire Devices“, is published in Nanoscale. This work demonstrates potential memory applications of Ag₂Te nanowires.
2/2019 Our review article, “Tuning spin-orbit coupling in 2D materials for spintronics: A topical review“, is published in Journal of Physics: Condensed Matter.
1/31/2019 Prof. Gao gave a physics colloquium at Northeastern University.
12/2018 Collaborative paper with Prof. Mohan Sankaran’s group published in ACS Appl. Mater. Interfaces: Direct, Transfer-Free Growth of Large-Area Hexagonal Boron Nitride Films by Plasma-Enhanced Chemical Film Conversion (PECFC) of Printable, Solution-Processed Ammonia Borane. Kasun from our group contributed to the work as the second author. congratulations.
12/2018 Lab alumnus Dr. Sukrit Sucharitakul gave an invited talk on behalf of Prof. Gao at the 2018 Nano-Micro Conference in Korea and received an Innovation Award for the work and presentation on 2D semiconductor InSe. Congrats, Sukrit.

11/5/2018 Prof. Gao visited Solon school district’s Parkside Elementary School to talk about Physics and Physics research to 2nd graders. The kids were thrilled to see the demonstration of magnetic levitation by high Tc superconductors and learn about liquid nitrogen.
10/2018 Our collaborative paper with UT Austin, “Effect of SrTiO₃ oxygen vacancies on the conductivity of LaTiO₃/SrTiO₃heterostructures“, is accepted by Journal of Applied Physics. Shuhao from our group contributed to the work. We thank Profs. Ekerdt and Demkov’s group for their collaboration and AFOSR for the funding support.
10/2018 Kyle’s paper “α-MoO3 as a Conductive 2D Oxide: Tunable n-Type Electrical Transport via Oxygen Vacancy and Fluorine Doping” is accepted by ACS Applied Nano Materials. Well done! We thank AFOSR for funding this work.
10/2018 Our latest paper on the new reentrant insulating phase (RIP) in correlated 2D systems appeared as a featured open-access review article in Applied Sciences. The authors include Richard (our honorable alumnus who discovered the RIP connected with the metal-insulator transition in low-density 2D holes in GaAs), Clara, and Shuhao.
9/2018 Clara (Chieh-Wen) published two insightful papers on topological crystalline insulator/band insulator SnTe/PbTe heterostructure, one in Physical Review B and the other in Nano Letters. We thank Profs. Zhidong Zhang and Song Ma of Chinese Academy of Sciences for their collaboration and NSF for funding our work.
- “Non-Drude Magneto-Transport Behavior in a Topological Crystalline Insulator/Band Insulator Heterostructure”, Nano Letters, 18 (10), 6538–6543 (2018). In this work, we reveal a novel non-Drude behavior of the topological Dirac electrons residing at the SnTe/PbTe interface.
- “Broken mirror symmetry tuned topological transport in PbTe/SnTe heterostructures“, Phys. Rev. B 98, 161301(R) (2018) (Rapid communication). This paper describes the control of magnetoresistance and the destruction of giant linear magnetoresistance by broken mirror symmetry in SnTe.

Our paper “Intrinsic Electron Mobility Exceeding 1000 cm^2/(V s) in Multilayer InSe FETs“, Sucharitakul et al, Nano Letters, 15, 3815-3819 (2015) is recognized as a highly cited paper according to Web of Science (“As of 2018, this highly cited paper received enough citations to place it in the top 1% of the academic field of Physics based on a highly cited threshold for the field and publication year.” )

6/14/2018 Xuan Gao has been promoted to the rank of full Professor. Many thanks to all the former and current group members for the contributions that helped Xuan achieving this!

6/3/2018 Kasun’s paper “Tuning Rashba Spin-Orbit Coupling in Gated Multi-layer InSe” has been accepted for publication in Nano Letters. Congrats Kasun for his first publication. (Also, in a high impact journal~)
5/20/2018 ShuHao Liu officially graduated. Congratulations Dr. Liu!

5/14/2018 Prof. Gao attends the AFOSR program review in Niceville, FL. A lot of nice discussions on 2D oxides!

4/20/2018 Collaborative paper ” Role of the different defects, their population, and distribution in the LaAlO₃/SrTiO₃ heterostructure’s behavior” is published online. This paper was also selected as an editor’s pick by JAP.

4/19/2018 Undergraduate student MoCun Ye is awarded a $4000 SURES summer research scholarship. We thank the Case Alumni Association for the support.

4/13/2018 Undergraduate student Yang Han wins Japanese Speech Contest. Well done!

4/6/2018 Case Daily highlights the publication and media attention on our SnSe work.
3/27/2018 The American Institute of Physics (AIP) published a press release (“Exploring the thermoelectric properties of tin selenide nanostructures“) accompanying our newly published SnSe paper in JAP. Our paper was chosen as one of about 10 to be highlighted by the AIP in March of all the papers that its journals publish. The news also appeared in other media outlets such as C&EN, phys.org , Sciencedaily, Nanowerk, EurekAlert, Physnews.com, Azonano, Sciencenewsline, Eelectroiq, and more.

3/27/1028 Our new paper “Nanostructured SnSe: Synthesis, doping, and thermoelectric properties“, is published in Journal of Applied Physics (Liu et al, Journal of Applied Physics 123, 115109 (2018)). In this paper, we report the study of growth and thermoelectric characterization of nanostructured SnSe, a promising thermoelectric material for converting waste heat into electricity. This work also bridges thermoelectrics and graphene-like two-dimensional materials, two major directions in condensed matter and material physics research.

3/20/2018 Shuhao Liu successfully defended his Ph.D. thesis. Congratulations!

3/5-3/9/2018 Our group visited Los Angeles to attend the annual meeting of American Physical Society. Clara, Shuhao, Kasun, and Kyle each gave a talk and Prof. Gao chaired a session on semiconductor nanowires, nanorods, and nanotubes.

2/18/2018 group dinner celebrating the lunar new year

2/2/2018 Case Daily news about our new collaborative research grant on layered 2D oxides from AFOSR.

10/8/2017 group lunch and foliage outing

10/3/2017 Shuhao gave an invited talk (on behalf of Prof. Xuan Gao) at the 232nd ECS meeting on the thermoelectric properties of IV-VI monochalcogenide nanostructures, see abstract here.

10/1/2017 Chieh-Wen (Clara) Liu joins our group as a postdoc scholar. Welcome, Clara! We also welcome undergraduate students Yang Han, Derek Tang who are doing their senior capstone projects in our group. Runtian Miao, a junior undergrad also started part-time research with our lab. Welcome, all!

9/28/2017 Xuan Gao gave a Physics Colloquium on layered 2D semiconductor and topological insulator materials at Kent State University.

8/2017 We recently published a few papers on topological insulator films in collaboration with Prof. Zhenhua Wang (former visiting scholar in our lab) and Prof. Zhidong Zhang at Chinese Academy of Sciences: “Electron delocalization and relaxation behavior in Cu-doped Bi₂Se₃ films” (Physical Review B); “From linear magnetoresistance of parabolic magnetoresistance in Cu and Cr-doped topological insulator Bi₂Se₃ films” (Jour. of Phys. and Chem. Solids); “Broadband photovoltaic effect of n-type topological insulator Bi₂Te₃ films on p-type silicon substrates” (Nano Research); “Fabrication and characterizations of Bi₂Te₃ based topological insulator nanomaterials” (book chapter in Outlook and Challenges of Nano Devices, Sensors, and MEMS. Springer International Publishing).

8/2017 A collaborative paper on ZnO nanowires with Prof. Juan Du (former postdoc in our lab) at Chinese Academy of Sciences was published in Jour of Mater Sci & Tech: “Control of ZnO nanowire growth and optical properties in a vapor deposition process“.

6/2017 Sukrit’s paper “V2O5: a 2D van der Waals Oxide with Strong In-plane Electrical and Optical Anisotropy” was accepted for publication in ACS Applied Materials & Interfaces. In this work, we report the largest in-plane electrical transport anisotropy effect in 2D materials to date. This work was a collaboration with Prof. Lambrecht (CWRU), Prof. Rui He (Univ. Northern Iowa) and Prof. Hilde Poelman (Ghent University, Belgium).

6/2017 We say farewell to Sukrit (Good luck to your new position at RIKEN!) and also welcome new graduate student Arvind Shankar joining our group.
5/2017 UIUC undergraduate Ryuji Fujita will be working in our group for a month. welcome back, Ryuji.
5/2017 Congratulations, Dr. Sucharitakul, the 4th Ph.D. from our lab!

5/2017 Xuan Gao attended the annual AFOSR project review at the Kirtland Airforce Base in Albuquerque.
4/2017 Undergraduate Physics major Mingyuan Wang receives a SOURCE/SURES research scholarship to do summer research in our lab. Congratulations!

4/2017 An article about our scanning photocurrent mapping of carrier diffusion in organo-metal halide perovskite solar cell material is published in the ‘TECH BEAT’ column of Tribology & Lubrication Technology magazine (page 12-13 in the April 2017 issue).
4/2017 X-mol.com and weixin.qq.com release a news article about our perovskite paper (in Chinese).

3/2017 Our paper, “Anisotropic electrical resistance in mesoscopic LaAlO₃/SrTiO₃devices with individual domain walls” is published in Scientific Reports of Nature Publishing Group. This work is a collaboration with Prof. Sehirlioglu’s group at CWRU’s Materials Science and Engineering and Prof. Marie-Hélène Berger at MINES Paris Tech, France.

1/2017 Our work on scanning photocurrent imaging microscopy of halide perovskite films made news at Case Daily, Phys.org, Sciencedaily and many other media outlets!

11/2016 Shuhao’s paper, “Imaging the Long Transport Lengths of Photo-generated Carriers in Oriented Perovskite Films”, has been accepted by Nano Letters, a leading journal in Nanoscience and technology. This work directly shows a surprisingly long diffusion length of carriers in halide perovskite, shedding light on the material’s remarkable performance in solar cell devices. Congratulations.! The just accepted paper can be downloaded here

10/2016 Xuan Gao was a plenary speaker at the Ohio-region section of the American Physical Society meeting. He presented the recent work by Shuhao Liu (in collaboration with Prof. Clemens Burda’s group) on scanning photocurrent microscopy imaging of photo-generated carrier diffusion in organo-metal halide perovskite films, a rising star photovoltaic material.

Positions Available

Motivated students are encouraged to contact Prof. Gao (xuan.gao @case.edu) if you are interested in working with us.

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Welcome to Xuan Gao’s Group Website

Our current research projects include:

Electron transport and phase transitions in correlated two-dimensional electron (or hole) system in semiconductor quantum wells.

Quantum confinement, spin-orbit coupling, topology/symmetry protection effects in topological states of matter (topological insulators, Dirac semi-metals etc).

Understanding the energy conversion processes in emerging materials relevant to renewable energy.

Nanowires or graphene-like atomically thin semiconductors for next-generation nanoelectronics, optoelectronics, or biosensors.

Please visit our research projects webpage for more details.

What’s New

Prof. Gao is taking a sabbatical leave at National Taiwan University as a visiting professor this Fall.

10/2020 Another publication for Arvind: “Interfacial Charge Transfer and Gate-Induced Hysteresis in Monochalcogenide InSe/GaSe Heterostructures” ACS Applied Materials & Interfaces 12 (41), 46854-46861 (2020). We also congratulate undergraduate coauthors Mingyuan, Yancheng, and Ryuji.

09/2020 Congratulations to Arvind on the publication of “Electron-electron interactions in the two-dimensional semiconductor InSe“Phys. Rev. B 102, 121301(R) (2020). Graduate student Kasun and undergraduate Min Gao were also coauthors.

08/2020 Congratulations to Kyle on the publication of “Electrical Characterization and Charge Transport in Chemically Exfoliated 2D LixCoO2 Nanoflakes”, The Journal of Physical Chemistry C, 124, 38, 20693–20700 (2020).

04/2020 Kyle Crowley defended his Ph.D. thesis online (due to the pandemic). Congratulations! Kyle will work with Dr. Ina Martin at the MORE center during the summer and then join NASA Glenn Research Center as a postdoctoral fellow.

12/2019 Clara’s invited topical review on topological nanomaterials, “Topical Review: Development of Topological Insulator and Topological Crystalline Insulator Nanostructures“, is published as Nanotechnology, 31, 192001 (2020). Congratulations.

12/2019 Our group published a few collaborative papers with the Chinese Academy of Sciences on topological insulator and 2D semiconductors:

11/2019 Kasun Premasiri defended Ph.D. thesis and will start as a postdoc fellow at Microsoft Station Q at Purdue University, working with our collaborator Prof. Michael Manfra. Congratulations and good luck, Kasun.

10/2019 Clara finishes her postdoc in the group and moves on to explore medical physics research with Dr. Ping Xia at Cleveland Clinic. Congratulations and good luck, Clara.

5/20/2019 Prof. Gao attended the annual AFOSR program review on 2D oxide project at Washington DC.

4/20/2019 Prof. Gao visited Harvard and gave a talk on nanowires with spin-orbit coupling at the CML symposium celebrating Prof. Charles (Charlie) Lieber‘s past and ongoing achievements. Happy Birthday, Charlie!

4/4/2019 Prof. Gao visited Ohio University and gave a seminar on 2D layered materials at the Nanoscale and Quantum Phenomena Institue.

3/8/2019 Prof. Gao gave an invited talk on monochalcogenides, a new family of graphene-like two-dimensional semiconductors with atomic thickness, at the annual March meeting of American Physical Society. Group members Kasun and Arvind also gave three contributed talks.

3/6/2019 Kasun’s work “Electrically Driven Structural Phase Transition in Single Ag2Te Nanowire Devices“, is published in Nanoscale. This work demonstrates potential memory applications of Ag2Te nanowires.

2/2019 Our review article, “Tuning spin-orbit coupling in 2D materials for spintronics: A topical review“, is published in Journal of Physics: Condensed Matter.

1/31/2019 Prof. Gao gave a physics colloquium at Northeastern University.

12/2018 Lab alumnus Dr. Sukrit Sucharitakul gave an invited talk on behalf of Prof. Gao at the 2018 Nano-Micro Conference in Korea and received an Innovation Award for the work and presentation on 2D semiconductor InSe. Congrats, Sukrit.

11/5/2018 Prof. Gao visited Solon school district’s Parkside Elementary School to talk about Physics and Physics research to 2nd graders. The kids were thrilled to see the demonstration of magnetic levitation by high Tc superconductors and learn about liquid nitrogen.

10/2018 Kyle’s paper “α-MoO3 as a Conductive 2D Oxide: Tunable n-Type Electrical Transport via Oxygen Vacancy and Fluorine Doping” is accepted by ACS Applied Nano Materials. Well done! We thank AFOSR for funding this work.

6/14/2018 Xuan Gao has been promoted to the rank of full Professor. Many thanks to all the former and current group members for the contributions that helped Xuan achieving this!

6/3/2018 Kasun’s paper “Tuning Rashba Spin-Orbit Coupling in Gated Multi-layer InSe” has been accepted for publication in Nano Letters. Congrats Kasun for his first publication. (Also, in a high impact journal~)

5/20/2018 ShuHao Liu officially graduated. Congratulations Dr. Liu!

5/14/2018 Prof. Gao attends the AFOSR program review in Niceville, FL. A lot of nice discussions on 2D oxides!

4/20/2018 Collaborative paper ” Role of the different defects, their population, and distribution in the LaAlO3/SrTiO3 heterostructure’s behavior” is published online. This paper was also selected as an editor’s pick by JAP.

4/19/2018 Undergraduate student MoCun Ye is awarded a $4000 SURES summer research scholarship. We thank the Case Alumni Association for the support.

4/13/2018 Undergraduate student Yang Han wins Japanese Speech Contest. Well done!

4/6/2018 Case Daily highlights the publication and media attention on our SnSe work.

3/20/2018 Shuhao Liu successfully defended his Ph.D. thesis. Congratulations!

3/5-3/9/2018 Our group visited Los Angeles to attend the annual meeting of American Physical Society. Clara, Shuhao, Kasun, and Kyle each gave a talk and Prof. Gao chaired a session on semiconductor nanowires, nanorods, and nanotubes.

2/18/2018 group dinner celebrating the lunar new year

2/2/2018 Case Daily news about our new collaborative research grant on layered 2D oxides from AFOSR.

10/8/2017 group lunch and foliage outing

10/3/2017 Shuhao gave an invited talk (on behalf of Prof. Xuan Gao) at the 232nd ECS meeting on the thermoelectric properties of IV-VI monochalcogenide nanostructures, see abstract here.

10/1/2017 Chieh-Wen (Clara) Liu joins our group as a postdoc scholar. Welcome, Clara! We also welcome undergraduate students Yang Han, Derek Tang who are doing their senior capstone projects in our group. Runtian Miao, a junior undergrad also started part-time research with our lab. Welcome, all!

9/28/2017 Xuan Gao gave a Physics Colloquium on layered 2D semiconductor and topological insulator materials at Kent State University.

8/2017 A collaborative paper on ZnO nanowires with Prof. Juan Du (former postdoc in our lab) at Chinese Academy of Sciences was published in Jour of Mater Sci & Tech: “Control of ZnO nanowire growth and optical properties in a vapor deposition process“.

6/2017 We say farewell to Sukrit (Good luck to your new position at RIKEN!) and also welcome new graduate student Arvind Shankar joining our group.

5/2017 UIUC undergraduate Ryuji Fujita will be working in our group for a month. welcome back, Ryuji.

5/2017 Congratulations, Dr. Sucharitakul, the 4th Ph.D. from our lab!

5/2017 Xuan Gao attended the annual AFOSR project review at the Kirtland Airforce Base in Albuquerque.

4/2017 Undergraduate Physics major Mingyuan Wang receives a SOURCE/SURES research scholarship to do summer research in our lab. Congratulations!

4/2017 An article about our scanning photocurrent mapping of carrier diffusion in organo-metal halide perovskite solar cell material is published in the ‘TECH BEAT’ column of Tribology & Lubrication Technology magazine (page 12-13 in the April 2017 issue).

4/2017 X-mol.com and weixin.qq.com release a news article about our perovskite paper (in Chinese).

1/2017 Our work on scanning photocurrent imaging microscopy of halide perovskite films made news at Case Daily, Phys.org, Sciencedaily and many other media outlets!

Positions Available

08/2020 Congratulations to Kyle on the publication of “Electrical Characterization and Charge Transport in Chemically Exfoliated 2D Li_xCoO₂ Nanoflakes”, The Journal of Physical Chemistry C, 124, 38, 20693–20700 (2020).

3/6/2019 Kasun’s work “Electrically Driven Structural Phase Transition in Single Ag₂Te Nanowire Devices“, is published in Nanoscale. This work demonstrates potential memory applications of Ag₂Te nanowires.

4/20/2018 Collaborative paper ” Role of the different defects, their population, and distribution in the LaAlO₃/SrTiO₃ heterostructure’s behavior” is published online. This paper was also selected as an editor’s pick by JAP.