Condensed Matter Seminar

All future


Wednesday, October 24th 2018
1:25 pm:
Speaker: Johnpierre Paglione, University of Maryland, College Park
Subject:  High-spin superconductivity in topological half-Heusler semimetals

In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The "spin" of a Bloch electron, however, is fixed by the symmetries of the crystal and the atomic orbitals from which it is derived, and in some cases can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing states to form beyond triplet, with higher spin quasi-particles combining to form quintet or even septet pairs. After reviewing experimental evidence for high-spin pairing in the exotic superconducting state of the half-Heusler compound YPtBi, I will introduce our recent work elucidating the influence of spin-orbit coupling on both the normal and superconducting states of this system

Faculty Host: Vlad Pribiag

Wednesday, October 31st 2018
1:25 pm:
Speaker: Adam Wei Tsen, University of Waterloo, Institute for Quantum Computing
Subject:  New Phase Transitions in Atomically Thin Quantum Materials

We have recently demonstrated an experimental platform to isolate 2D quantum materials that are unstable in the ambient environment. I will discuss our studies of the Weyl semimetal candidate, 1T’-MoTe2, and layered magnetic insulator, CrI3, in the atomically thin limit, made possible using this technique. In MoTe2, lowering dimensionality suppresses the inversion symmetric monoclinic phase, driving the Weyl ground state up to and beyond room temperature. The different electronic structure of thin samples is studied by magnetotransport measurements at low temperature. In CrI3, we observe a very large negative magnetoresistance effect that is quantitatively comparable to colossal magnetoresistance in the manganites. I will explain the origin of this effect and discuss some new opportunities for other 2D magnets.

Faculty Host: Ke Wang

Wednesday, November 7th 2018
1:25 pm:
Speaker: Jason Petta, Princeton University
Subject: Microwave Spectroscopy of Valley States in Silicon

The bulk conduction band of Si has six equivalent valleys. Strain in Si/SiGe heterostructures partially lifts the six-fold valley degeneracy by raising the energy of the four in-plane valleys. It is known that large electric fields can lift the degeneracy of the remaining two low-lying valleys. However, the measured valley splittings range from 10 – 300 μeV, suggesting that microscopic details such as interface roughness and disorder impact the valley splitting. In this lecture I will describe how microwave spectroscopy can be applied to probe valley states in silicon nanostructures [1]. In the first experiment, a cavity coupled Si double quantum dot is probed using microwave frequency photons. The transmission of the photons through the microwave cavity displays signatures that are consistent with the valley degree of freedom and the data can be modeled using cavity input-output theory [2]. We also use Landau-Zener interferometry to probe the low-lying energy level structure of a silicon double quantum dot. The observed Landau-Zener interference pattern persists down to low driving frequencies of 50 MHz, suggesting relatively long-lived charge coherence. Low-lying valley states result in a unique Landau-Zener interference pattern that is in contrast with measurements on conventional two-level charge qubits [3]. These new probes of valley states have high energy resolution and may be applied to other low energy degrees of freedom.

1. Burkard and Petta, PRB 94, 195305 (2016).
2. Mi, Peterfalvi, Burkard, and Petta, PRL 119, 176803 (2017).
3. Mi, Kohler, and Petta, PRB 98, 161404(R) (2018).

Faculty Host: Ke Wang

Wednesday, November 14th 2018
1:25 pm:
Speaker: Mathias Scheurer, Harvard University
Faculty Host: Rafael Fernandes

Wednesday, November 28th 2018
1:25 pm:
Speaker: Kimberley Hill, CEGE
Faculty Host: James Kakalios

Wednesday, December 5th 2018
1:25 pm:
Speaker: Damjan Pelc
Faculty Host: Martin Greven

Wednesday, December 12th 2018
1:25 pm:
Speaker: Brian Skinner, MIT
Faculty Host: Boris Shklovskii

Wednesday, January 30th 2019
1:30 pm:
Speaker: Turab Lookman, Los Alamos National Lab
Faculty Host: Martin Greven

Wednesday, February 27th 2019
1:30 pm:
Speaker: Joerg Schmalian, Karlsruhe Institute of Technology
Faculty Host: Rafael Fernandes

Wednesday, April 3rd 2019
1:25 pm:
Speaker: Graeme Luke, McMaster University
Faculty Host: Martin Greven

Wednesday, May 1st 2019
1:25 pm:
Speaker: Jack Harris, Yale University
Subject: TBD
Faculty Host: Paul Crowell

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