Welcome!

Welcome to The Frustrated and Quantum Magnetism group and the Ross lab in the Department of Physics at Colorado State University.

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.

We use neutron scattering to directly probe the static and dynamic correlations in such materials. Neutron scattering has the advantage of providing directional and energy-resolved information, which can be successfully and simply compared with theory. Through collaborations with solid state chemists and condensed matter theorists, we strive to push the boundaries of magnetic solids towards strongly quantum entangled states.

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

Ross lab attended FRAMS 2019 where Kate gave an invited talk.

Student Awards

Gavin wins best poster award at the 5th Front Range Advanced Magnetics Symposium. Photo credit: Ron Goldfarb

Recent results

A Novel Strongly Spin-Orbit Coupled Quantum Dimer Magnet: Yb2Si2O7

October 31, 2018August 14, 2019

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…

Short-range order in the quantum XXZ honeycomb lattice material BaCo2(PO4)2

April 14, 2018April 14, 2018

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…

Tuning the antiferromagnetic helical pitch length and nanoscale domain size in Fe3PO4O3 by magnetic dilution

February 14, 2018

We have investigated the effect of magnetic dilution (substituting Ga for Fe) on the partially ordered helical antiferromagnetic ground state of Fe3PO4O3. The helical state in this compound is known to form in needle-like domains, with short range correlations in the ab plane. Our most recent results, published in PRB, show that the helical pitch length and the ab plane correlation length are intrinsically related to each other – the pitch length appears to set the size of the correlations in the ab plane. This is reminiscent of Skyrmions, whose size is set by the helical pitch length.

News

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!
Aug. 2019: Ross lab attends the 5th Front Range Advanced Magnetics Symposium in Boulder, CO where Kate gave an invited talk and Gavin won a best poster award for his work on Yb2Si2O7.
Jul. 2019: Danielle attends the 25th CHRNS Summer School on Methods and Applications of Neutron Spectroscopy.
Jun. 2019: Gavin wins a best presentation award at the 6th annual PRSE Magnetics Workshop held at CSU for his work on a new quantum dimer magnet Yb2Si2O7.
Apr. 2019: The iQuantum He3 insert was installed on the Quantum Design MPMS XL.
Mar. 2019: Daniel Shaw joins the group as a graduate researcher and Steffen Säubert joins as a postdoctoral researcher. Welcome Daniel and Steffen!
Jan. 2019: Danielle wins a best poster prize award at the NHMFL 2019 Spring Theory Winter School for her work on Er2Sn2O7.
Aug. 2018: Andrew Treglia and John Ringler join the group as graduate researchers. Welcome Andrew and John!
Jul. 2018: Kate, Gavin, Colin and Danielle attended the 2018 Highly Frustrated Magnetism conference in Davis, CA. Gavin and Colin gave poster presentations while Kate was honored at an Oxford Instruments banquet.
Jun. 2018: Kate received the DOE Early Career award which will fund her research on non-equilibrium effects in quantum magnets through 2023.
Apr. 2018: Owen Ross Neilson joins the group as an honorary researcher! Welcome Owen!
Feb. 2018: Kate wins the Oxford Instruments 2018 Lee Osheroff Richardson prize.
Jan. 2018: Danielle Yahne joins the group as a graduate researcher. Welcome Danielle!
Feb. 2017: Kate is appointed as Communications Secretary for the Neutron Scattering Society of America for a 3 year term.
Jan. 2017: Colin Sarkis joins the group as a graduate researcher. Welcome Colin!
Oct. 2016: Tyler Dodge wins a best student poster prize at the APS Four Corners section meeting in Las Cruces, NM, for his work on Resonant Ultrasound Spectroscopy.
Oct. 2016: Kate wins the 2016 APS George E. Valley Jr. Prize.
Aug. 2016: Tyler Dodge wins a best student poster prize at FRAMS (Front Range Magnetics Symposium) for his work on Resonant Ultrasound Spectroscopy.
Jul. 2016: Kate is appointed a CIFAR Global Scholar and joints the CIFAR Quantum Materials program for a 2 year term.
May 2016: Cory Berg joins the group as an undergraduate researcher and Gavin Hester joins the group as a graduate researcher. Welcome Cory and Gavin!
Feb. 2016: Dr. Hari Nair joins the group. Welcome Hari!
Jan. 2016: Tim Reeder joins the group as an undergraduate researcher, and Jake Walker joins the group as a graduate researcher. Welcome Tim and Jake!
Jan. 2016: Optical Floating Zone Furnace installed in Ross lab
Nov. 2015: Kate was elected to the SNS-HFIR User Group Executive Committee (SHUG-EC) for a 3 year term.
Nov. 2015: Jesse attended his first neutron scattering experiment at the NIST Center for Neutron Research.
Oct. 2015: Jesse attended the APS Four Corners Meeting in Arizona and presented a poster about his ongoing research project.
Jul. 2015: Jesse and Kate attended the Kavli Institute for Theoretical Physics (KITP) meeting “Novel States in Spin–Orbit Coupled Quantum Matter”. Kate spoke about her recent work on Yb2Ti2O7.
Jun. 2015: Kate spoke at the Gordon Research Conference on Neutron Scattering, held in Hong Kong.
Mar. 2015: Kate gave an invited talk at the APS March Meeting in San Antonio, TX, on a new pyrochlore project: NaCaCo2F7
Jan. 2015: Kate taught at the Winter Theory School in Tallahassee, see slides from the school, including my lecture on “Experimental Pyrochlore Systems” here.
Nov. 2014: Kate received the Alice Wilson award from the Royal Society of Canada. From the RSC website: “The three Alice Wilson Awards are presented annually to women of outstanding academic qualifications … who are entering a career in scholarship or research at the postdoctoral level.”
Sep. 2014: Kate signed on as Assistant Professor in the Department of Physics at Colorado State University, beginning August 2015.
Sep. 2014: Kate took up an NSERC Post Doctoral Fellowship at Colorado State University, working in the Neilson Lab in the Department of Chemistry. She worked on crystal growth and synthesis, particularly on the material Fe3PO4O3.
Jun. 2014: Kate was awarded the 2014 Prize for Outstanding Student Research from the Neutron Scattering Society of America, and presented at the American Conference of Neutron Scattering (ACNS).

Publication highlights

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).
Neutron Laue Diffraction Study on the Magnetic Phase Diagram of Multiferroic MnWO4 under Pulsed High Magnetic Fields. Phys. Rev. Lett., 106, 237202 (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)

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