Prof. Sara Haravifard

Department of Physics

Duke University

Host: Kaul

Title: Investigating real-world quantum spin liquid candidates

Abstract: The quantum spin liquid (QSL) state is an exotic state of matter featuring a high degree of entanglement and lack of long-range magnetic order in the zero-temperature limit.  Recently, Yb-based triangular lattice antiferromagnets have garnered significant interest as possible QSL candidates, however, the presence of chemical disorder in real-world compounds has made directly measuring the Hamiltonian parameters challenging. To further elucidate role of chemical disorder and to explore phase diagram of these materials, we present neutron scattering and high-resolution magnetometry measurements of YbMgGaO4 and YbZnGaO4, covering a broad range of applied magnetic field at low temperature. We use key observations of the magnetic phase crossover to motivate an exploration of the field- and parameter-dependent phase diagram, providing an expanded view of the available magnetic states in applied field. More broadly, our approach demonstrates a means of pursuing QSL candidates where Hamiltonian parameters might otherwise be obscured by disorder. 

Prof. Sara Haravifard

Department of Physics

Duke University

Host: Kaul

Title: Investigating real-world quantum spin liquid candidates

Abstract: The quantum spin liquid (QSL) state is an exotic state of matter featuring a high degree of entanglement and lack of long-range magnetic order in the zero-temperature limit.  Recently, Yb-based triangular lattice antiferromagnets have garnered significant interest as possible QSL candidates, however, the presence of chemical disorder in real-world compounds has made directly measuring the Hamiltonian parameters challenging. To further elucidate role of chemical disorder and to explore phase diagram of these materials, we present neutron scattering and high-resolution magnetometry measurements of YbMgGaO4 and YbZnGaO4, covering a broad range of applied magnetic field at low temperature. We use key observations of the magnetic phase crossover to motivate an exploration of the field- and parameter-dependent phase diagram, providing an expanded view of the available magnetic states in applied field. More broadly, our approach demonstrates a means of pursuing QSL candidates where Hamiltonian parameters might otherwise be obscured by disorder. 

Prof. Adrian Del Maestro

Department of Physics and Astronomy

University of Tennessee

Host: Kaul

Title: Nanoscale confinement towards a one-dimensional superfluid

Abstract: In one spatial dimension, enhanced thermal and quantum fluctuations should preclude the existence of any long range ordered superfluid phase of matter.  Instead, the quantum liquid should be described at low energies by an emergent hydrodynamic framework known as Tomonaga-Luttinger liquid theory.  In this talk I will present details on some orthogonal but complimentary experimental and theoretical searches for this behavior in helium-4 including: (1) pressure driven superflow through nanopores, and (2) the excitation spectrum of a confined superfluid inside nano-engineered porous silica-based structures. For flow experiments, we have devised a framework that is able to quantitatively describe dissipation at the nanoscale leading to predictions for the critical velocity borne out by recent superflow measurements in nanopores.  In confined porous media, with radii reduced via pre-plating with rare gases, I will discuss ab initio simulations of phase and density correlations inside the pore that are in agreement with recent neutron scattering measurements.   Taken together, these results indicate significant progress towards the experimental observation of a truly one-dimensional quantum liquid.

This work was supported by the NSF through grants DMR-1809027 and DMR-1808440.

Prof. Adrian Del Maestro

Department of Physics and Astronomy

University of Tennessee

Host: Kaul

Title: Nanoscale confinement towards a one-dimensional superfluid

Abstract: In one spatial dimension, enhanced thermal and quantum fluctuations should preclude the existence of any long range ordered superfluid phase of matter.  Instead, the quantum liquid should be described at low energies by an emergent hydrodynamic framework known as Tomonaga-Luttinger liquid theory.  In this talk I will present details on some orthogonal but complimentary experimental and theoretical searches for this behavior in helium-4 including: (1) pressure driven superflow through nanopores, and (2) the excitation spectrum of a confined superfluid inside nano-engineered porous silica-based structures. For flow experiments, we have devised a framework that is able to quantitatively describe dissipation at the nanoscale leading to predictions for the critical velocity borne out by recent superflow measurements in nanopores.  In confined porous media, with radii reduced via pre-plating with rare gases, I will discuss ab initio simulations of phase and density correlations inside the pore that are in agreement with recent neutron scattering measurements.   Taken together, these results indicate significant progress towards the experimental observation of a truly one-dimensional quantum liquid.

This work was supported by the NSF through grants DMR-1809027 and DMR-1808440.

Dr. Paul McClarty

Max Planck Institute for the Physics of Complex Systems

Dresden, Germany

Host: Kaul

Title: Topological Magnons

Abstract: Coherent magnetic excitations can have nontrivial topological features. In this talk, I'll give examples of "gapped" and "gapless" band topology of magnons including Kitaev-Heisenberg honeycomb models as analogues of Chern insulators and Dirac nodal lines in CoTiO3. Then I'll talk about features of band topology that are special to magnon systems: (i) the robustness of topological edge states in the presence of interactions; (ii) the visualization of spin-momentum locking in neutron scattering; (iii) the non-Hermitian topology of spontaneous magnon decay.

Dr. Paul McClarty

Max Planck Institute for the Physics of Complex Systems

Dresden, Germany

Host: Kaul

Title: Topological Magnons

Abstract: Coherent magnetic excitations can have nontrivial topological features. In this talk, I'll give examples of "gapped" and "gapless" band topology of magnons including Kitaev-Heisenberg honeycomb models as analogues of Chern insulators and Dirac nodal lines in CoTiO3. Then I'll talk about features of band topology that are special to magnon systems: (i) the robustness of topological edge states in the presence of interactions; (ii) the visualization of spin-momentum locking in neutron scattering; (iii) the non-Hermitian topology of spontaneous magnon decay.

Dr. Lucia Steinke

National High Magnetic Field Laboratory High B/T Facility

University of Florida

Host: Gannon

Title: Towards a universal measurement platform for calorimetric and thermal transport measurements at the combined extremes of high magnetic fields and sub-millikelvin temperatures

Abstract: The NHMFL High B/T facility at the University of Florida in Gainesville pursues the mission to enable user experiments at the combined extremes of high magnetic fields B and ultra-low temperatures (ULT) below one millikelvin. While almost all measurement techniques like electrical transport or magnetometry require adaptations to be successfully performed in this environment, calorimetry and thermal transport are particularly challenging due to a lack of suitable thermometry. Existing thermometers typically either lack ULT sensitivity, are incompatible with high magnetic fields, or have too high masses and long thermalization times to allow for measurements of small samples. Specific heat and thermal transport experiments at ULT and high B - especially on small crystals - would be essential to studies of quantum criticality, superconductors with very low transition temperatures, or to provide evidence for a quantum spin liquid state. To meet increased user demand for such experiments, our group is developing fast and compact ULT thermometers to form the basis of a universal measurement platform for calorimetry and thermal transport of a variety of samples. The measurement principle relies on the well-established temperature dependent viscosity of liquid ³He that is probed by tracking the resonance of quartz tuning forks immersed in the liquid. I will report on recent progress in the miniaturization of such tuning fork thermometers (TFT), and present results from field and temperature dependent performance tests. 

The National High Magnetic Field Laboratory is supported by the National Science Foundation through NSF DMR-1644779 and the State of Florida.

Dr. Lucia Steinke

National High Magnetic Field Laboratory High B/T Facility

University of Florida

Host: Gannon

Title: Towards a universal measurement platform for calorimetric and thermal transport measurements at the combined extremes of high magnetic fields and sub-millikelvin temperatures

Abstract: The NHMFL High B/T facility at the University of Florida in Gainesville pursues the mission to enable user experiments at the combined extremes of high magnetic fields B and ultra-low temperatures (ULT) below one millikelvin. While almost all measurement techniques like electrical transport or magnetometry require adaptations to be successfully performed in this environment, calorimetry and thermal transport are particularly challenging due to a lack of suitable thermometry. Existing thermometers typically either lack ULT sensitivity, are incompatible with high magnetic fields, or have too high masses and long thermalization times to allow for measurements of small samples. Specific heat and thermal transport experiments at ULT and high B - especially on small crystals - would be essential to studies of quantum criticality, superconductors with very low transition temperatures, or to provide evidence for a quantum spin liquid state. To meet increased user demand for such experiments, our group is developing fast and compact ULT thermometers to form the basis of a universal measurement platform for calorimetry and thermal transport of a variety of samples. The measurement principle relies on the well-established temperature dependent viscosity of liquid ³He that is probed by tracking the resonance of quartz tuning forks immersed in the liquid. I will report on recent progress in the miniaturization of such tuning fork thermometers (TFT), and present results from field and temperature dependent performance tests. 

The National High Magnetic Field Laboratory is supported by the National Science Foundation through NSF DMR-1644779 and the State of Florida.

Prof. Divine Kumah

Department of Physics

North Carolina State University

Host: Gannon

Title: Tuning Transport and Magnetism at Polar Oxide Interfaces

Abstract: Atomic-scale interactions at the interfaces between polar and non-polar transition metal oxides have led to the realization of exciting phenomena including two-dimensional electron gases, superconductivity and interfacial magnetism. However, these interactions may lead to the suppression of electronic and magnetic ordering at interfaces with strong structure-property relationships. By imaging the atomic structure of the interface between polar LaSrMnO3 (LSMO) and non-polar SrTiO3, we identify interfacial structural distortions which are correlated with thickness-dependent metal-insulator and ferromagnetic-paramagnetic transitions in the rare-earth manganites. We show that these structural distortions can be tuned by inserting polarity-matched spacer layers at the LSMO interfaces leading to a stabilization of ferromagnetism in LSMO layers as thin as two unit cells. The stabilized magnetism is found to be independent of strain. We employ a combination of synchrotron X-ray diffraction, temperature-dependent magnetization measurements and X-ray magnetic circular dichroism to elucidate the interplay between structural and spin degrees of freedom in the rare-earth manganites.[1,2] Additionally, we find that by tuning growth and post-growth processing conditions, a two-dimensional electron gas (2DEG) forms at the interface between antiferromagnetic LaCrO3 and SrTiO3 providing a route to design all-oxide heterostructures which couple magnetic ordering with the mobile carriers within the 2DEG.[3] These results demonstrate the intimate role of picometer-scale structural distortions on the physical properties of transition metal oxides and have important implications for designing novel quantum materials.

References



[1] Koohfar et. al., npj Quantum Materials 4 (1), 25 (2019)

[2] Koohfar et. al., Physical Review B 101 (6), 064420 (2020)

[3] Al-Tawhid et. al., AIP Advances 10 (4), 045132 (2020)

Prof. Divine Kumah

Department of Physics

North Carolina State University

Host: Gannon

Title: Tuning Transport and Magnetism at Polar Oxide Interfaces

Abstract: Atomic-scale interactions at the interfaces between polar and non-polar transition metal oxides have led to the realization of exciting phenomena including two-dimensional electron gases, superconductivity and interfacial magnetism. However, these interactions may lead to the suppression of electronic and magnetic ordering at interfaces with strong structure-property relationships. By imaging the atomic structure of the interface between polar LaSrMnO3 (LSMO) and non-polar SrTiO3, we identify interfacial structural distortions which are correlated with thickness-dependent metal-insulator and ferromagnetic-paramagnetic transitions in the rare-earth manganites. We show that these structural distortions can be tuned by inserting polarity-matched spacer layers at the LSMO interfaces leading to a stabilization of ferromagnetism in LSMO layers as thin as two unit cells. The stabilized magnetism is found to be independent of strain. We employ a combination of synchrotron X-ray diffraction, temperature-dependent magnetization measurements and X-ray magnetic circular dichroism to elucidate the interplay between structural and spin degrees of freedom in the rare-earth manganites.[1,2] Additionally, we find that by tuning growth and post-growth processing conditions, a two-dimensional electron gas (2DEG) forms at the interface between antiferromagnetic LaCrO3 and SrTiO3 providing a route to design all-oxide heterostructures which couple magnetic ordering with the mobile carriers within the 2DEG.[3] These results demonstrate the intimate role of picometer-scale structural distortions on the physical properties of transition metal oxides and have important implications for designing novel quantum materials.

References



[1] Koohfar et. al., npj Quantum Materials 4 (1), 25 (2019)

[2] Koohfar et. al., Physical Review B 101 (6), 064420 (2020)

[3] Al-Tawhid et. al., AIP Advances 10 (4), 045132 (2020)