SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Atac Imamoglu
Moire superlattices in two dimensional semiconductors have enabled the observation of a wealth of phenomena driven by strong electronic correlations, ranging from Mott-Wigner states to quantum anomalous Hall effect. In this talk, I will describe magnetic properties of van der Waals heterostructures forming a frustrated triangular lattice in the vicinity of Mott-insulator states of electrons. By directly measuring electronic magnetization through the strength of the polarization-selective attractive polaron resonances, we find that when the Mott state is electron doped, the system exhibits ferromagnetic correlations in agreement with Nagaoka model. Our observations, which are in agreement with DMRG calculations, provide a direct evidence for itinerant magnetism with a kinetic origin.
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Martin Claassen
Irradiation with light provides a powerful tool to interrogate, control or induce quantum states in solids, however a microscopic understanding of light-matter coupling in interacting electron systems remains a profound challenge. In this talk, I will discuss how quantum geometry can grant a new handle and design principle to steer and probe strongly-correlated quantum materials using light, whereby photons must dynamically dress and deform the effective Wannier orbitals that comprise the material's interacting bands. This effect is generic to all interacting electron systems, however can dominate optical properties in materials with non-trivial quantum geometry or topology, leading to poorly-localized or obstructed Wannier functions. I will discuss ramifications for spectroscopic responses in flat-band materials and THz driving of moiré heterostructures such as twisted bilayer graphene, and argue that ultrafast pump-probe experiments can provide a new avenue to explore the rich phase diagram of these materials out of equilibrium.
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Suyang Xu
Quantum geometry - the geometry of electron Bloch wavefunctions - is central to modern condensed matter physics. Due to the quantum nature, quantum geometry has two parts, the real part quantum metric and the imaginary part Berry curvature. Berry curvature has led to countless breakthroughs, ranging from the quantum Hall effect in 2DEGs to the anomalous Hall effect (AHE) in ferromagnets. In contrast, the quantum metric has rarely been explored. In this talk, I will report a new nonlinear Hall effect induced by quantum metric dipole by interfacing even-layered MnBi2Te4 with black phosphorus. This nonlinear Hall effect switches direction upon reversing the AFM spins. It exhibits distinct scaling demonstrating the non-dissipative nature. Like the AHE brought Berry curvature under the spotlight, our results open the door to discovering quantum metric responses. Moreover, our data suggests that the AFM can harvest wireless electromagnetic energy, enabling applications that bridges nonlinear electronics with AFM spintronics.
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Jiun-Haw Chu
Weyl semimetals (WSMs) are three-dimensional topological materials that exhibit fascinating properties due to the presence of Weyl nodes in their band structure, including the chiral anomaly, Fermi arcs, and an intrinsic anomalous Hall effect. However, existing WSMs discovered so far often possess multiple pairs of Weyl nodes, posing a challenge in disentangling the contributions to transport phenomena from different energy bands and mechanisms. To overcome this challenge, we have identified field-induced ferromagnetic MnBi2-xSbxTe4 as an ideal type-II WSM with a single pair of Weyl nodes. In this talk, I will discuss how we resolved the evolution of Fermi-surface sections as the Fermi level is tuned across the charge neutrality point by employing a combination of quantum oscillations and high-field Hall measurements. I will also discuss the discovery of a singular, heartbeat-like behavior in the anomalous Hall conductivity as the Fermi level is tuned across the Weyl nodes, a unique feature previously predicted theoretically for a type-II WSM. Our findings establish MnBi2-xSbxTe4 as an ideal and tunable platform for further investigation into Weyl physics.
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Justin Song
Light is most often utilized as a versatile probe of quantum matter. However, when it strongly interacts with materials, new collector behavior not found in either the irradiating light or in the electronic material individually can emerge. In this talk, I will describe how light can strongly alter the state and behavior of matter producing interesting light driven ferroic phases and novel collective behavior.
*Funding Acknowledgement: This work is funded by Singapore MOE Academic Research Fund Tier 3 Grant MOE2018-T3-1-002.
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Carsten Putzke
In the pursuit to develop new and more powerful electronics, semiconductor research has pushed the sample size over many decades to the nanometer scaler now aiming for single electron transistors. By achieving this, new length scales have become more important leading to hydrodynamic, ballistic and quantum transport phenomena. To realize these regimes in strongly correlated electron systems requires samples in the order of a few micrometers even in high quality single crystals. To achieve this, we use focused ion beam (FIB) machining. This gives us control of sample shape, size and current path orientation with nanometer precision.
In the first part of my talk I will show you how finite size confinement allows us to achieve precise current flow in highly anisotropic crystals. With this we can demonstrate the particle-like (ballistic, in-plane) and wave-like (phase coherent, out-of-plane) nature of the electronic transport in the anisotropic, single band metal PdCoO2 [1,2]. By using angle dependent magnetic field measurements of the out-of-plane transport we can further demonstrate the crossover from finite size to bulk transport regime (see figure below). I will give an outlook how this finding can open a new route to study the elusive Pseudogap in high purity cuprate superconductors [3].
1: Bachmann, et al. Nat. Comm. 10, 5081 (2019).
2: Putzke, et al. Science 368, 1234 (2020).
3: Putzke, et al. Nature Physics (2021).
SPICE Workshop on Non-equilibrium Quantum Materials Design, June 27th - 29th 2023
Marios H. Michael
Light control of materials is a leading frontier in Condensed Matter research, aiming to create new material properties at will. One of the most ambitious goal in this field is to photo-induce superconductivity above Tc. I will discuss how coupling phonons to inter-band electron transitions can drive a paradigm shift in this field. This coupling naturally generates attraction proportional to phonon fluctuations, which can be enhanced through driving. Resonant amplification of this attraction occurs when the electronic gap and phonon frequency align closely in energy. I will present how this model can explain long-lived superconductivity observed in pumped K3C60 and then explain how this simple model can be used to explicitly design new photo-induce superconducting devices using 2D materials coupled to surface plasmons.
https://arxiv.org/abs/2303.15355 : Mechanisms for Long-Lived, Photo-Induced Superconductivity, Sambuddha Chattopadhyay ... Marios H. Michael
Alexey Berdyugin
In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy, whereas the filled bands underneath contribute little to conduction. Here, we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics that resemble those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common to all graphene-based superlattices.
