Tuning J$_1$-J$_2$ in Quasi-2D Triangular Lattice Antiferromagnet $\alpha$-SrCr$_2$O$_4$ via Uniaxial Pressure

Triangular lattice antiferromagnets first attracted attention as a frustrated magnetic lattice which can serve as a platform to realize the resonating valence bond state. While the triangular lattice itself was shown to support classical 120 degree order, many theoretical phase diagrams suggest a quantum spin liquid state within a small range of parameters. One possible avenue to achieve such a state is to tune the anisotropy of the triangular lattice antiferromagnet by applying uniaxial pressure. This motivated our Raman scattering study of quasi-two-dimensional antiferromagnet $\alpha$-SrCr$_2$O$_4$ under applied uniaxial pressure. Under ambient conditions, $\alpha$-SrCr$_2$O$_4$ develops long-range helical magnetic order below T$_N$ = 43 K. We identify two-magnon excitations associated with this long-range antiferromagnetic order below T$_N$ at 15.5 meV and 40 meV by comparison with spin wave calculations. We observe the two features from the two-magnon excitation shift away from (towards) each other under applied tensile (compressive) pressure, indicating a decrease (increase) in anisotropy. Raman active phonons show a shift to higher (lower) frequencies under applied compressive (tensile) pressure, indicating efficient transmission of pressure and tuning of the lattice. We show spin wave and two-magnon density of states calculations under uniaxial pressure are consistent with our experimental results.