Events on Thursday, January 22nd, 2026
- R. G. Herb Condensed Matter Seminar
- Coulomb Drag Studies of Interacting Luttinger Liquids
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin Hall, hosted by Tiancheng Song
- Speaker: Mingyang Zheng, University of Florida
- Abstract: One-dimensional (1D) quantum wires provide a powerful platform for exploring strong electron–electron interactions and collective excitations under extreme confinement. Coulomb drag between coupled 1D systems offers a uniquely sensitive probe of Tomonaga–Luttinger liquid (TLL) physics, yet some of the central drag theoretical predictions have remained experimentally untested. In the first part of this talk, I will introduce the Coulomb drag measurement technique and present our earlier results on tunable reciprocal and nonreciprocal Coulomb drag in vertically coupled quantum wires, including drag in the nonlinear regime. These studies establish a flexible platform in which Coulomb drag contributions can be tuned by gate voltage and temperature, and they provide a robust experimental route to extracting TLL interaction parameters in realistic, multichannel quantum wires. In the second part of the talk, I will discuss our most recent work on Coulomb drag in the presence of a perpendicular magnetic field. Using magnetic depopulation, we characterize the gate-dependent electron density in individual 1D wires. We find that the magnetic-field dependence of the drag resistance exhibits clear oscillations that align with the depopulation of 1D subbands. Moreover, the observed downturn in the high-temperature Arrhenius activation behavior and the corresponding upturn in the intermediate-temperature power-law exponent are consistent with Coulomb drag between density-mismatched 1D wires. I will conclude with a brief overview of earlier work from my previous group on electrically controlled spin-polarized light-emitting diodes based on a 2D CrI₃/hBN/WSe₂ heterostructure, highlighting connections to spin-dependent transport and hybrid low-dimensional systems.
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Nonlinear Saturation of Ballooning Modes in Stellarators
- Time: 1:00 pm
- Place: Sterling Hall B343
- Speaker: Xu Chu , PPPL
- Abstract: The nonlinear evolution and saturated states of ballooning modes – in particular, metastable states – are critical for understanding explosive MHD events in magnetic confinement fusion (MCF) devices, such as edge-localized modes (ELMs) in tokamaks and core density collapses (CDCs) in LHD. In this work, ballooning mode saturation is investigated in realistic stellarator configurations using the flux tube approach of Ham et. al. [1]. The method is adapted to account for the lack of exact force balance in stellarator equilibrium solvers that assume existence of nested flux surfaces. A variational approach for calculating flux tube energy is developed to overcome this force error problem in stellarator numerical equilibria. Saturated (equilibrium) flux tube states that cross 10-20% of the plasma minor radius are shown to exist for linearly ballooning unstable profiles. It is shown that several features of the displaced flux tube structure in a full nonlinear MHD simulation of Wendelstein 7X are reproduced by our model. Saturated states are found in a compact stellarator equilibrium close but below the marginal ballooning linear instability, i.e. the unperturbed equilibrium is metastable. This suggests that Edge-Localized-Mode-like explosive MHD behavior may be possible in stellarators.
[1] Ham C J, Cowley S C, Brochard G and Wilson H R 2018 Plasma Physics and Controlled Fusion 60 075017
- Host: Tony Qian