Research Themes
Our research focuses on emergent phenomena in correlated electronic materials. We focus on the synthesis (i.e. crystal growth) and characterization, via neutron scattering, of strongly interacting magnetic materials. A particularly exciting goal of this research is to realize what is known as the Quantum Spin Liquid state, where magnetic moments dance together in an entangled, correlated, but ultimately disordered and dynamic way.
Crystals with magnetic degrees of freedom offer enormous diversity of emergent phenomena arising from simple near-neighbor interactions in a vast group of magnetic ions (~1023 of them!). Dynamics ranging from “classical” spin waves that propagate a spin flip through an array of aligned moments, to emergent photon-like excitations that mimic electrodynamics, can be created, probed, and understood in this environment.
New Capabilities Coming Online
Our group is developing a home-built resonant ultrasound spectroscopy (RUS) insert for the PPMS that will operate at fields up to H=9T and temperatures down to T=2K, with help from Prof. Leisure (CSU) and the Ultrasound group lead by Albert Migliori (Los Alamos National Lab). We successfully acquired our first low temperature RUS spectrum in Jan 2018 and look forward to using this new tool.
Recent Adventures
Gavin and Danielle attended a polarized neutron spectroscopy workshop hosted by Oak Ridge National Lab. Ross lab attended FRAMS 2019 where Kate gave an invited talk. Colin and Steffen went to the NHMFL in Tallahassee, FL to run an experiment on the 30T magnet. Danielle Yahne, Gavin Hester, and Colin Sarkis all presented their recent work at the 2019 Materials Research Society Spring meeting…
Student Awards
Danielle wins award for outstanding student presentation at APS 4CS meeting. Gavin wins best poster award at the 5th Front Range Advanced Magnetics Symposium. Photo credit: Ron Goldfarb Gavin’s talk, titled “A Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb2Si2O7”, wins a Best Presentation award at the Summer… Danielle Yahne wins Best Poster award at the National High Magnetic Field Lab’s 2019 Theory Winter School in Tallahassee, FL….
Recent results
Recently published in Physical Review B: Magnetic frustration in Fe3PO4O3 produces an unusual magnetic state below Tn = 163K, where incommensurate antiferromagnetic order is restricted to nanosized needle-like domains. We report our single crystal neutron diffraction work, which show continuous rings of scattering in the ab-plane with a well-defined radius. Our analysis show Fe3PO4O3 does not choose a preferred ordering wavevector direction, despite having a fixed magnitude. We reproduce a quasi-degenerate manifold of ordering wavevectors using an antiferromagnetic Heisenberg model with nearest and second neighbor interactions. The state shows a stark similarity to the partially ordered phase of the skyrmion… Recently published in Physical Review Letters: The quantum dimer magnet (QDM) is the canonical example of “quantum magnetism”. We report our single crystal neutron diffraction, specific heat, and ultrasound velocity work on a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb2Si2O7. These measurements reveal a gapped singlet zero field ground state with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of Hc1 ~0.4 T and Hc2 ~1.4 T. These results raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of… Recently published in Physical Review B: The magnetic honeycomb lattice with competing interactions can give rise to unconventional quantum phases. We present observations of highly frustrated quasi two-dimensional (2D) magnetic correlations in the honeycomb lattice layers of the Seff = 1/2 compound BaCo2(PO4)2. Specific heat lacks a sharp anomaly down to 2K although all spin entropy is recovered, indicating the absence of a transition to long range order in this material. However, ac susceptibility shows that spins do not freeze into a spin-glass like state. The spin correlations measured by neutron powder diffraction reveal short range quasi-2D order with…Partial antiferromagnetic helical order in single-crystal Fe3PO4O3
A Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb2Si2O7
Short-range order in the quantum XXZ honeycomb lattice material BaCo2(PO4)2
News
- Sep. 2020: Daniel successfully passed his master’s exam! Congrats Daniel!
- Aug. 2020: Ross lab attended the virtual workshop “Neutrons & Complementary Techniques for Quantum Materials“, hosted by ORNL. Kate gave a presentation on using heat capacity and ultrasound velocity measurements in the context of Yb2Si2O7.
- Aug. 2020: Members of Ross lab attended the 6th Front Range Advanced Magnetics Symposium virtually, hosted by Colorado School of Mines.
- Jul. 2020: Ross lab attended the virtual 2020 American Conference on Neutron Scattering (ACNS). Steffen, Colin, Danielle and Gavin gave presentations on their recent work. Gavin won an award for the best student oral presentation in hard matter, nice job Gavin!
- Jul. 2020: John performed our lab’s first remote neutron scattering experiment!
- May 2020: Ross lab attended the CIFAR Quantum Materials meeting virtually. Steffen, Colin, Danielle and Gavin gave poster presentations, and the question/discussion portion took place on Slack.
- Apr. 2020: Andrew successfully passed his master’s exam! Congrats Andrew!
- Feb. 2020: John successfully passed his master’s exam! Congrats John!
- Jan. 2020: Danielle has been nominated as the graduate student member of the SNS/HFIR User Group Executive Committee. Congrats Danielle!
- Dec. 2019: Gavin’s work on Yb2Si2O7 was featured on the Oak Ridge National Lab website in an article titled “Neutrons probe ultra-cold condensate for insight into quantum matter.” Check it out!
- Nov. 2019: Gavin’s work on Yb2Si2O7 was featured in a Physics Buzz article titled “The New Playground of an Unexpected Bose-Einstein Condensate.” Check it out!
- Oct. 2019: Kate won the CSU College of Natural Sciences Early Career Faculty Excellence in Undergraduate Teaching award! Congrats Kate!
- Oct. 2019: Gavin, Danielle, John, and Daniel attended the 2019 APS Four Corners Section Meeting. Gavin gave an invited talk as a finalist for the Harry Lustig award, and Danielle won a prize for an outstanding student presentation.
- Sep. 2019: Gavin and Danielle attend the Polarized Neutron Diffraction and Spectroscopy: Applications to Quantum Materials Workshop at Oak Ridge National Laboratory.
- Sep. 2019: Theo Wecker joins the group as a graduate researcher. Welcome Theo!
Publication highlights
- Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb2Si2O7. Phys. Rev. Lett. 123, 027201 (2019)
- Nanosized Helical Domains in Strongly frustrated Fe3PO4O3. Phys. Rev. B 92, 134419 (2015)
- Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique. Phys. Rev. B 86, 174424 (2012)
- Order by Quantum Disorder in Er2Ti2O7. Phys. Rev. Lett. 109, 167201 (2012)
- Quantum Excitations in Quantum Spin Ice. Phys. Rev. X 1, 021002 (2011).
Some invited talks online
- “”Quantum Spin Ice” Physics Determined from High Field Spin Wave Excitations in Yb2Ti2O7”: Exotic Phases of Frustrated Magnets, Kavli Institute for Theoretical Physics (KITP), Santa Barbara CA (October 2012)
- “Effective Spin-1/2 Hamiltonians Determined for Er2Ti2O7 & Yb2Ti2O7 Through Inelastic Neutron Scattering”: 4-Corner Condensed Matter Symposium, Perimeter Institute, Waterloo ON (May 2012)