2023 Abstracts NQMD

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Liuyan Zhao

Surface is present in any finite-size material systems, and its impact on phase transitions can be quite unconventional and interesting. Theory predicted a few decades ago that surface can undergo a phase transition into an ordered state at a higher temperature than bulk does when the interaction strength at the surface exceeds that inside the bulk – named as surface and extraordinary phase transitions for surface and bulk, respectively. Van der Waals (vdW) layered magnets provide a unique platform for potentially realizing such a stringent and rare condition. In this presentation, we use a combination of second order nonlinear optics, transport, and transmission electron microscopy to investigate CrSBr, a vdW layered antiferromagnet. We report our finding of surface and extraordinary phase transitions in CrSBr that are separated by 8K.

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Susanne Stemmer

In this talk, we will discuss the synthesis of high-quality thin films of cadmium arsenide (Cd₃As₂), which we grow by molecular beam epitaxy.  Cd₃As₂ is known to belong to a class of topological materials known as three-dimensional Dirac semimetals, but, as we will discuss in this presentation, in thin films it can be tuned between a variety of topological phases.  We will discuss the evolution of the electronic states of Cd₃As₂ films as their thickness is scaled.  We show that magnetotransport studies can distinguish between the different topological phases.  We will also discuss hybrid structures with superconductors that are an attractive route towards a topological superconductor.

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Claudia Felser

Chirality is a very active field of research in organic chemistry, closely linked to the concept of symmetry. Topology, a well-established concept in mathematics, has nowadays become essential to describe condensed matter [1,2]. At its core are chiral electron states on the bulk, surfaces and edges of the condensed matter systems, in which spin and momentum of the electrons are locked parallel or anti-parallel to each other. Magnetic and non-magnetic Weyl semimetals, for example, exhibit chiral bulk states that have enabled the realization of predictions from high energy and astrophysics involving the chiral quantum number, such as the chiral anomaly, the mixed axial-gravitational anomaly and axions [3-5].  Chiral topological crystals exhibit excellent chiral surface states [6,7] and different orbital angular momentum for the enantiomers, which can be advantageous in catalysis. The potential for connecting chirality as a quantum number to other chiral phenomena across different areas of science, including the asymmetry of matter and antimatter and the homochirality of life, brings topological materials to the fore [8].

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SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Richard Averitt

We will discuss our recent results using mid-to-near-IR pulses to initiate dynamics in correlated antiferromagnets. This includes cuprate and iridate compounds. The goal is to probe and control low energy modes (both lattice and spin) and to ascertain the impact on coupled degrees of freedom, including subtle changes in the electronic structure.

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

 Gil-Ho Lee       

Engineering quantum states through light-matter interaction has created a new paradigm in condensed matter physics. A representative example is the Floquet-Bloch state, which is generated by time-periodically driving the Bloch wavefunctions in crystals. Previous attempts to realize such states in condensed matter systems have been limited by the transient nature of the Floquet states produced by optical pulses, which masks the universal properties of non-equilibrium physics. I will introduce our recent effort on the generation of steady Floquet Andreev (F-A) states in graphene Josephson junctions by continuous microwave application and direct measurement of their spectra by superconducting tunnelling spectroscopy [1]. We present quantitative analysis of the spectral characteristics of the F-A states while varying the phase difference of superconductors, temperature, microwave frequency and power. We hope that this study can provide a basis for understanding and engineering non-equilibrium quantum states in dissipative condensed matter systems.

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Angel Rubio

We will  introduce our newly developed quantum electrodynamics density-functional formalism (QEDFT) as a first principles framework to predict, characterize and control the spontaneous appearance of ordered phases of strongly interacting light-matter hybrids. We will pursue the question whether it is possible to create these new states of materials as groundstates of the system. To this end we will show how the emerging (vacuum) dressed states resembles Floquet states in driven systems. We will discuss the potential to realize non-equilibrium states of matter that have so far been only accessible in ultrafast and ultrastrong laser-driven materials. We illustrate the realization of those ideas in molecular complexes and 2D materials and show that the combination of cavity-QED and 2D twisted van der Waals heterostructures provides a novel and unique platform for the seamless realization of a plethora of interacting quantum phenomena, including exotic and elusive correlated and topological phases of matter.

SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023

Wanzheng Hu

Multiferroics simultaneously exhibit ferroelectric and magnetic order that are intrinsically coupled to each other within a single phase. These couplings allow for the control of magnetization and polarization through respective cross-coupled electric and magnetic fields, which makes them appealing candidates for encoding and accessing information using two order parameters at a time.

Ultrashort laser pulses provide the possibility to generate large electric field strengths, which in turn allows for ultrafast switching of order parameters on sub-picosecond timescales. Experimental realization of intense terahertz (THz) and mid-infrared (MIR) pulses opens up new pathways for dynamical materials engineering. The strong electric fields of THz and MIR pulses are able to drive phonon oscillations with large amplitudes, where anharmonic contributions of the interatomic potential energy surface become important. These anharmonicities can be utilized to induce nonlinear phononic rectification, in which nonlinear coupling between phonon modes leads to a quasistatic distortion of the crystal structure, to induce transient crystal geometries that are not accessible in equilibrium. In this talk, I will present our recent results on the ultrafast manipulation of multiferroic BiFeO₃ by nonlinear phononics.