Event Time:
Wednesday, January 20, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/64320901982?pwd=ZFRVUnNVM0I2ckhYRDJnRlM4MjVBUT09 Passcode: 606472
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2021-01-20T12:00:00
2021-01-20T13:00:00
Imaging phonon-mediated hydrodynamic flow in WTe2 with cryogenic quantum magnetometry
Event Information:
Hydrodynamic electron flow, where electrons in a conductor flow collectively - akin to a fluid, is a unique signature of strong electron interactions in a material. This effect has been observed in 2D materials, but observations in bulk materials are intriguing as high-carrier density should screen the interactions. In this talk, I will discuss a recent measurement of hydrodynamic flow in the semimetal WTe2, allowing us to gain insight into the microscopic origin of its electron interactions.
We image the spatial profile of the electric current by using a nitrogen-vacancy scanning tip. Using coherent quantum sensing, we obtain magnetic field resolution of ~10nT and spatial resolution of ~100nm. The current pattern we observe differs substantially from the flat profile of a normal metal, and indicates correlated flow through the semimetal. The pattern also shows non-monotonic temperature dependence, with hydrodynamic effects peaking at ~20 K.
We compare our results to a model which combines ab initio electron scattering rates and the electronic Boltzmann transport equation.
The model shows quantitative agreement with our measurement, allowing us to extract the strength of electron-electron interactions in our material. Furthermore, we conclude that electron interactions are phonon-mediated. This result opens a path for hydrodynamic flow and strong interactions in a variety of new materials.
Event Location:
https://ubc.zoom.us/j/64320901982?pwd=ZFRVUnNVM0I2ckhYRDJnRlM4MjVBUT09 Passcode: 606472
Event Time:
Monday, January 25, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/66194846742?pwd=STlJSFhUOEZBWUM2OEpkWHB5VEZ0QT09 Passcode: 038461
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2021-01-25T12:00:00
2021-01-25T13:00:00
Electrical probes of non-Abelian spin liquids
Event Information:
Recent thermal-conductivity measurements evidence a magnetic-field-induced non-Abelian spin liquid phase in the Kitaev material α-RuCl3. In this talk, I will explain how we leverage fermion condensation to propose a series of measurements for electrically detecting the hallmark chiral Majorana edge states and bulk anyons in the spin-liquid phase -- despite the fact that α-RuCl3 is a good Mott insulator. In particular, I introduce circuits that exploit interfaces between electronic systems and α-RuCl3 to convert physical fermions into emergent fermions, thus enabling analogs of transport and probes of non-Abelian-anyon physics in topological superconductors. I will also explain how we developed an anyon-interferometry framework that incorporates nontrivial energy-partitioning effects. These results illuminate a partial pathway toward using Kitaev materials for topological quantum computation.
Event Location:
https://ubc.zoom.us/j/66194846742?pwd=STlJSFhUOEZBWUM2OEpkWHB5VEZ0QT09 Passcode: 038461
Event Time:
Wednesday, January 27, 2021 | 12:00 pm - 1:00 pm
Event Location:
https://ubc.zoom.us/j/65104619882?pwd=UE80WkY4RXdEMFMxU2VCbEFwaXhjdz09 Passcode: 428347
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2021-01-27T12:00:00
2021-01-27T13:00:00
Monopolar and dipolar relaxation in classical spin ice
Event Information:
The quantum spin liquid is a hypothesized state characterized by macroscopic entanglement and fractionalized quasiparticles. While the physical realization of long-range entanglement of spins remains elusive, the phenomenon of spin fractionalization has been exemplified by magnetic monopoles in classical spin ice. In this talk, I will discuss how we experimentally distinguish emergent monopoles from individual spin dipoles through magnetic relaxation dynamics of spin ice Ho2Ti2O7. Combining time-resolved neutron scattering and broad-band magnetometry, we have probed over ten decades of time scales and uncovered a thermal crossover between two distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of spin dipoles. Disorders serve as a tuning parameter of monopole mobility, suggesting a potential controlling method of achieving coherent monopole dynamics in quantum spin ice.
Reference
Y. Wang et al., Monopolar and dipolar relaxation in spin ice Ho2Ti2O7, arXiv: 2011.06477 (2020)
Event Location:
https://ubc.zoom.us/j/65104619882?pwd=UE80WkY4RXdEMFMxU2VCbEFwaXhjdz09 Passcode: 428347