Jian Xu thesis defense

Congratulations to Jian Xu for successfully defending his PhD thesis "The Dynamics of Random Field Ising Model". 

Thesis abstract:

The Random Field Ising Model (RFIM) is a general tool to study disordered systems. Crackling noise is generated when disordered systems are driven by external forces, spanning a broad range of sizes. Systems with different microscopic structures such as disordered magnets and Earth's crust have been studied under the RFIM. In this thesis, we investigated the domain dynamics and critical behavior in two dipole-coupled Ising ferromagnets Nd2Fe14B and LiHoxY1−xF4. With Tc well above room temperature, Nd2Fe14B has shown reversible disorder when exposed to an external transverse field and crosses between two universality classes in the strong and weak disorder limits. Besides tunable disorder, LiHoxY1−xF4 has shown quantum tunneling effects arising from quantum fluctuations, providing another mechanism for domain reversal. Universality within and beyond power law dependence on avalanche size and energy were studied in LiHo0.65Y0.35F4.

Related papers:

"Barkhausen …

Press release on two recent quantum ordering papers

From the Caltech Press Office

Manipulating Quantum Order

Cool a material to sufficiently low temperatures and it will seek some form of collective order. Add quantum mechanics or confine the geometry and the states of matter that emerge can be exotic, including electrons whose spins arrange themselves in spirals, pinwheels, or crystals.

In a recent pair of publications in Nature Communications, teams led by Caltech's Thomas F. Rosenbaum, professor of physics and holder of the Sonja and William Davidow Presidential Chair, report how they have combined magnetic fields and large pressures to not only induce these states at ultra-low temperatures, but also to nudge them between competing types of quantum order.

Links to technical papers:

"Spiral magnetic order and pressure-induced superconductivity in transition …

PPMS Dynacool now online

Our newest piece of major instrumentation, this is a cryogen-free hellum flow cryostat, with temperature controllable between 1.7 and 400 K, and magnetic fields …

Moving Day!

We moved from Chicago. 2 semi trailers filled with equipment and other stuff. A crane lowered it all down into the Sloan subbasement. It took a week to unload.

New article in Nature Physics on correlated electrons

Charge ordering in metals is a fundamental instability of the electron sea, occurring in a host of materials and often linked to other collective ground states …