We explore the response of Ir 5d orbitals to pressure in β-Li2IrO3, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit (SO) interaction in 5d orbitals, pushes β-Li2IrO3 further away from the pure J eff = 1/2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to realization of a QSL state in this hyperhoneycomb iridate at high pressures.The novel electronic ground states of 5d-based compounds driven by spin-orbit interactions continue to provide an excellent playground for the realization of unconventional quantum phases of matter including topological insulators [1-4] and quantum spin-liquids (QSLs) [5][6][7]. One example of the latter is the non-trivial QSL ground state of the Kitaev model [8], a rare example of a solvable interacting quantum model with Majorana fermions as its elementary excitations. Material candidates for possible realization of the Kitaev model include honeycomb-based-lattice systems with strong spin-orbit coupling [6,9], such as the two and three-dimensional honeycomb iridates, α-Li(Na) [7,[20][21][22] as well as α-RuCl 3 [23,24]. However, it is experimentally established that these materials order magnetically at low temperatures [17,18,20,[25][26][27], spoiling numerous attempts to realize the Kitaev QSL. Hence, tuning structure and related intricate interactions present in these materials through chemical or physical pressure provides a potential route to introduce magnetic frustration and realize novel phases of matter.In this Letter we have investigated the electronic and structural response of β-Li 2 IrO 3 to high pressure. Xray absorption near edge structure (XANES) measurements at Ir L-edges reveal a dramatic suppression of the isotropic Ir (L 3 /L 2 ) branching ratio at P ∼ 1.5 GPa, signaling a reduction in the effective strength of spinorbit interactions in the 5d band. This is the same pressure at which net magnetization in applied field collapses [17]. The reconstructed electronic state preserves the L z / S z orbital-to-spin moment ratio of Ir magnetic moments and the insulating ground state indicating that spin-orbit interactions and Mott physics con-

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Transport and magnetic studies of PbTaSe 2 under pressure suggest the existence of two superconducting phases with the low temperature phase boundary at ∼ 0.25 GPa that is defined by a very sharp, first order, phase transition. The first order phase transition line can be followed via pressure dependent resistivity measurements, and is found to be near 0.12 GPa near room temperature. Transmission electron microscopy and x-ray diffraction at elevated temperatures confirm that this first order phase transition is structural and occurs at ambient pressure near ∼ 425 K.The new, high temperature / high pressure phase has a similar crystal structure and slightly lower unit cell volume relative to the ambient pressure, room temperature structure. Based on firstprinciples calculations this structure is suggested to be obtained by shifting the Pb atoms from the 1a to 1e Wyckoff position without changing the positions of Ta and Se atoms. PbTaSe 2 has an exceptionally pressure sensitive, structural phase transition with ∆T s /∆P ≈ −1400 K/GPa near room temperature, and ≈ −1700 K/GPa near 4 K. This first order transition causes an ∼ 1 K (∼ 25%) step -like decrease in T c as pressure is increased through 0.25 GPa.