Two-dimensional triangular-lattice materials with spin-1/2 are perfect platforms for investigating quantum frustrated physics with spin fluctuations. Here we report the structure, magnetization, heat capacity and inelastic neutron scattering (INS) results on cesium ytterbium diselenide, CsYbSe2. There is no long-range magnetic order down to 0.4 K at zero field. The temperature dependent magnetization, M (T ), reveals an easy-plane magnetic anisotropy. A maximum is found in M (T ) around T ∼1.5 K when magnetic field H is applied in the ab plane, indicating the short-range interaction. The low-temperature isothermal magnetization M (H) shows a one-third plateau of the estimated saturation moment, that is characteristic of a two-dimensional frustrated triangular lattice. Heat capacity shows field-induced long-range magnetic order for both H||c and H||ab directions. The broad peak in heat capacity and highly damped INS magnetic excitation at T =2 K suggests strong spin fluctuations. The dispersive in-plane INS, centered at the (1/3 1/3 0) point, and the absence of dispersion along c direction suggests 120 • non-collinear 2D-like spin correlations. All these results indicate that the two-dimensional frustrated material CsYbSe2 can be in proximity to the triangularlattice quantum spin liquid. We propose an experimental low-temperature H-T phase diagram for CsYbSe2.

A triangular lattice selenide series of rare earths (RE), CsRESe 2 , were synthesized as large single crystals, using a flux growth method. This series stabilized in either trigonal (R3̅ m) or hexagonal (P6 3 /mmc) crystal systems. Physical properties of CsRESe 2 were explored by magnetic susceptibility and heat capacity measurements down to 0.4 K. Antiferromagnetic interaction was observed in all magnetic compounds, while no long-range magnetic order was found, indicating the frustrated magnetism. CsDySe 2 presents spin freezing at 0.7 K, revealing a spin-glass state. CsCeSe 2 and CsYbSe 2 present broad peaks at 0.7 and 1.5 K, respectively, in the magnetization, suggesting the shortrange interactions between magnetic RE ions. The lack of signature for long-range magnetic order and spin freezing down to 0.4 K in these compounds (RE = Ce, Yb) implies their candidacy for a quantum spin liquid state.

In this paper we report the synthesis, magnetization and heat capacity of the frustrated magnets AErSe2(A=Na,K) which contain perfect triangular lattices of Er 3+ . The magnetization data suggests no long-range magnetic order exists in AErSe2(A=Na,K), which is consistent with the heat capacity measurements. Large anisotropy is observed between the magnetization within the ab plane and along the c axis of both compounds. When the magnetic field is applied along ab plane, anomalies are observed at 1.8 µB in NaErSe2 at 0.2 T and 2.1 µB in KErSe2 at 0.18 T. Unlike NaErSe2, a plateau-like field-induced metamagnetic transition is observed for H c below 1 K in KErSe2. Two broad peaks are observed in the heat capacity below 10 K indicating possible crystal electric field(CEF) effects and magnetic entropy released under different magnetic fields. All results indicate that AErSe2 are strongly anisotropic, frustrated magnets with field-induced transition at low temperature. The lack of signatures for long-range magnetic order implies that these materials are candidates for hosting a quantum spin liquid ground state.

A series of transition metal vanadate crystals were prepared using a high temperature (580 ˚C) hydrothermal method. The compounds all had the general formula A 2 AEM(VO 4) 2 (A = K, Na, Li; AE = Ba, Sr; M = Co, Fe, Mn). They are all variations of the glaserite structural type and range in symmetry from P-3m1 to P-3 to P2 1 /c. Most of the derivatives contain a planar threefold rotation operation, making them possible spin frustration candidates. Single crystal structural analyses were performed on many of the derivatives to obtain a detailed understanding of the distortions of the tetrahedral building blocks that accommodate the symmetry distortions. A hydrothermal growth method was developed to grow high quality single crystals of sizes up to 2-3mm/edge. This method can be generalized for large crystal growth to enable magnetic and neutron diffraction studies that require relatively large single crystals.

Ultrafast laser physics continues to advance at a rapid pace, driven primarily by the development of more powerful and sophisticated diode-pumping sources, the development of new laser materials, and new laser and amplification approaches such as optical parametric chirped-pulse amplification. The rapid development of high average power cryogenic laser sources seems likely to play a crucial role in realizing the long-sought goal of powerful ultrafast sources that offer concomitant high peak and average powers. In this paper, we review the optical, thermal, thermo-optic and laser parameters important to cryogenic laser technology, recently achieved laser and laser materials progress, the progression of cryogenic laser technology, discuss the importance of cryogenic laser technology in ultrafast laser science, and what advances are likely to be achieved in the near-future.