Research

  • Theory/AI/ML-guided materials design, synthesis and characterizations
  • Chiral fermions in condensed matters
  • Topological phase transitions
  • Strain and pressure tuning of quantum phenomena
  • Unconventional superconductivity
  • Superconducting and topological electronics/qubits
  • Quantum dots spin qubits
  • Superconducting materials, critical current, and devices for magnets and energy applications
  • Thermoelectric materials and applications
  • Crystal growth and spark plasma synthesis (pressure synthesis)
  • CVD, sputtering, and pulsed laser deposition of thin films (Laser MBE at BNL)
  • Time- and angular-resolved photoemission spectroscopy (tr-ARPES at BNL)
  • Real-time visualization of magnetic field by magneto-optical imaging (MOI)
  • First-principles calculations of electronic materials

An example of magnetic field distribution in a superconducting film captured by our home-made MOI system

Magneto-Optical Imaging of dentritic magnetic flux jump in carbon-doped superconducting magnesium diboride thin film at 4.2 K and perpendicular external field of 10 mT (zero-field-cooled film, size of 5 mm X 5 mm)

More about MOI can be found in the Ph. D thesis of Zuxin Ye, who received one of the 2005 President’s Awards to Distinguished Doctoral Students.

Chiral fermions in condensed matters and applications

Chiral fermions in condensed matter systems: (a) A Dirac semimetal (purple) hosts both left-handed (LH)- and right-handed (RH)-fermions on the same band. A Weyl semimetal (blue and orange) hosts LH- and RH-fermions on separate bands. (b) The definition of chirality in relativistic quantum field theory. (c) Chiral qubits have two base states describing chiral fermions circulating clockwise and counter-clockwise. (d) The chiral anomaly is manifested, e.g., as the chiral magnetic effect – generation of an electric current by external gauge fields with non-trivial topology (e.g. by parallel electric and magnetic fields) – The signature of the chiral magnetic effect is the negative longitudinal magnetoresistance first discovered in Dirac semimetal ZrTe_5 [Q. Li et al, arXiv:1412.6543 (2014); Nature Physics 12, 550 (2016).] (e) The chiral photovoltaic cell enables a production of electric current in a Weyl semimetal via circular photogalvanic effect. (f) Chiral transduction uses chirality as encoder/decoder in transmitting a message, and serves as a “quantum bus” between quantum devices operating at different frequencies.

Detailed explanations can be found in the article by Q. Li “Dynamics of chiral fermions in condensed matter systems” Nobel Symposium Proceedings on Chiral Matters (2021)

Equipment:

  • Pulsed Laser Deposition system (BNL)

Atomic Layer-by-layer Pulsed Laser Deposition system has an excimer laser (Compex 201: KrF, 248nm, 700mJ/pulse, 10Hz), a six-target rotator for in-situ target exchange during deposition. Substrate temperatures can be held at up to 1000 °C, at pressures from 10-7 Torr to 1 Torr. A UHV chamber has base pressure 1×10-9 Torr. An ozone generator is used to provide ozone for better oxygenation of oxide films. A 20 kV RHEED system is used to monitor thin-film deposition to ensure layer-by-layer growth. A second chamber is also used for thin film growth.

  • MOD (Metal Organic Deposition) system is a programmable spin coater combination system (Model Cee 200) that features auto tuning PID and digital control.
  • A Spark Plasma Synthesis (SPS) for pressure synthesis (SPS2000, the first installation in North America | SUGA Co., Ltd.)
  • Inductively Coupled Plasma provides the atomic emission spectroscopy for highly sensitive and accurate determination of composition (Jobin Yvon Horiba Ultima).
  • Focused laser beam thin film patterning systems, while photolithography patterning systems and focused electron beam patterning systems are available at BNL’s CFN.
  • Oxford dilution refrigerator with 9-1-1 Tesla vector field superconducting magnet and optical access with 10 mK base temperature (BNL)
  • There are one MPMS (Magnetic Property Measurement System) magnetometer, and three PPMS (Physical Property Measurement System) made by Quantum Design for transport, thermodynamic, and magnetic property characterizations (BNL)

7T MPMS magnetometer has an ultra-low field option, rotator, a sample space furnace insert (up to 500 °C), and ac magnetization measurement option.

14 T PPMS (I) has Dilution Refrigerator (DR) Option for continuous operation from 4 K down to 60 mK, with compatible heat capacity, AC susceptibility for DR, and electrical transport measurements, horizontal and vertical rotators, optical multipurpose probes, and thermal transport option (TTO) for measurements of the Seebeck (and Nernst) coefficient and thermal conductivity,

9T PPMS (II) has a Helium-3 refrigerator option for continuous operation down to 0.5 K, and allows for resistivity and heat capacity measurements in an applied field up to 9 T, at temperatures between 1.8 K and 400 K, with additional measurement options for AC electric transport, thermal transport option (TTO) for measurements of specific heat, the Seebeck (and Nernst) coefficient and thermal conductivity, and critical current.

9T PPMS (III) with compatible heat capacity, electrical transport and DC resistivity measurements.

  • Time- and angular-resolved photoemission spectroscopy (tr-ARPES at BNL)
  • An arc furnace
  • A commercial melt spinner (Model SC made by Edmund Buhler)
  • A hot press (temperature up to 1800 °C under 4 GPa for samples up to 500 mm3 volume)
  • A ball mill and a Spex mill
  • A few dozens of box and tube furnaces for single crystal growth and materials synthesis
  • A few home-made probes for critical current measurements up to 1kA
  • A few strain probes custom-made for single crystals, thin films, and commercial superconducting wires and tapes capable of low temperature and high field operations
  • A few stand-alone superconducting magnets
  • A home-made low temperature magneto-optical imaging system for imaging magnetic structures, and magnetic field profiles in superconductors

Our basic science research at Stony Brook University and Brookhaven National Laboratory is primarily funded by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Materials Sciences and Engineering Division.

Additional funding for quantum information science is provided by the US Air Force Office of Scientific Research.

Additional funding for energy applications is provided by the US DOE Office of Energy Efficiency & Renewable Energy.

Additional funding for microelectronics is provided by the Stony Brook Research Foundation.

Additional funding for quantum materials for quantum networks is provided by the Stony Brook University Center for Distributed Quantum Processing (CDQP).