Condensed Matter Seminars This Term

The pursuit of quantum spin liquid (QSL) states in condensed matter physics has drawn attention to kagome antiferromagnets (AFM) where a two-dimensional corner-sharing network of triangles frustrates conventional magnetic orders. While quantum kagome AFMs based on Cu2+ (3d9, s=½) ions have been extensively studied, there is so far little work beyond copper-based systems. Here we present our bulk magnetization, specific heat and neutron scattering studies on single crystals of a new titanium fluorides Cs8RbK3Ti12F48 where Ti3+ (3d1, s = ½) ions form a modulated quantum kagome antiferromagnet that does not order magnetically down to 1.5 K. Our comprehensive map of the dynamic response function S(Q,ℏw) acquired at 1.5 K where the heat capacity is T-linear reveals a dispersive continuum emanating from soft lines that extend along (100). The data indicate fractionalized spinon-like excitations with quasi-one-dimensional dispersion within a quasi-two-dimensional spin system.

Mono and Bi layer graphene provide a platform

to study gapless Dirac points with linear and quadratic dispersion respectively.
The quadratic dispersion is analogous to non-relativistic particles in free space, while the linear is analogous to massless particles in free space.
In 2d electron gasses in FETs, it is known that the transport can be described by a shallow water hydrodynamics.
Variants which include momentum damping, as well as account for thermal transport, can be developed.
Hydrodynamics generally has a number of interesting phenomena, but here we focus on choking, which in the above mentioned FET case causes current saturation.

In the graphene case, near the dirac point, the bands above and below the dirac point lead to the electron and hole fluids, and a two fluid hydrodynamics approach is needed.

Motivated by remarkable properties of superfluid edge dislocations in solid Helium-4—responsible for the unique supertransoprt-through-solid and “syringe” effects, 

we reveal a broad class of quantum systems—boundaries in phase separated lattice states, magnetic domain walls, and ensembles of Luttinger liquids—that can be classified as transverse quantum fluids.  

Transverse quantum fluids provide us with a striking demonstration of conditional character of many dogmas associated with superfluidity, such as the necessity of elementary excitations, in general, 

and the ones obeying Landau criterion in particular, as well as the absence of long-range order in one-dimensional quantum superfluids.

Hydrogen will play an important role as the cleanest energy source in the future. How to produce, transport, and store hydrogen is an important issue. Meanwhile, hydrogen is also an ideal coolant for cooling the high temperature superconductor for power transmission and storage, and also for superfast transit for people and goods. In this presentation, I will discuss the development of efficient catalysts for hydrogen production through water electrolysis, transport and storage, and superfast vehicles traveling at about 400 miles per hour with absolute flexibility and safety.

Ultrahigh thermal conductivity has been constantly pursued for many applications. Diamond has the highest thermal conductivity but is an insulator, silicon and GaAs are good semiconductors used for our daily life but the thermal conductivity is too low, the band gap is not large enough nor the carrier mobility. Boron arsenide was theoretically predicted to have a unique combination of thermal conductivity close to that of diamond, a band gap as large as 2 eV, and equally high mobility in both electrons and holes. In this talk, I will present our progress on boron arsenide single crystals.