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A plethora of correlated and exotic metallic states have been identified on the border of itinerant magnetism, where the long-range spin texture is melted by tuning the magnetic transition temperature (T$_C$) towards zero, referred to as the quantum phase transition (QPT). So far, the study of QPT in itinerant magnets has mainly focused on low-T$_C$ materials (i.e., typically T$_C$ ~ 10 K) where the modification of electronic band structure is subtle, and only makes a small contribution to the QPT. Here we report a distinct example of a magnetic QPT accompanied by a gigantic modification of the electronic structure in FeGe, i.e., a well-studied itinerant chiral magnet hosting near-room-temperature (T$_C$ = 278 K) helical/skyrmion spin texture. The pressure-driven modification of the band structure (e.g., reduction of exchange splitting) is evidenced by magneto-transport study, suggesting a Fermi-surface reconstruction around the magnetic QPT (P ~19 GPa), in stark contrast to the case of typical metallic ferromagnets. Further application of pressure leads to a metal-to-insulator transition above P > 30 GPa, as also corroborated by our density-functional theory (DFT) calculation. Of particular interest is the occurrence of anomalous magneto-transport in the inhomogeneous short-range chiral-spin ground state (P = 20-30 GPa) above the QPT, with longitudinal fluctuations of magnetization. The unexpected observation of spontaneous anomalous Hall effect in this exotic quantum regime suggests macroscopic time-reversal symmetry (TRS) breaking, even in the absence of long-range magnetic order. Our findings mark the large body of unexplored high-T$_C$ itinerant magnets with broken inversion-symmetry as promising candidates of novel ground state formation near QPT.

We report a systematic study of Sm valence in the prototypical intermediate valence compound SmB$_6$. Sm mean valence, $v_{\rm Sm}$, was measured by X-ray absorption spectroscopy as functions of pressure ($1

FeSe with the PbO structure is a key member of the family of new high-$T_c$ iron pnictide and chalcogenide superconductors, as while it possesses the basic layered structural motif of edge-sharing distorted FeSe$_4$ tetrahedra, it lacks interleaved ion spacers or charge-reservoir layers. We find that application of hydrostatic pressure first rapidly increases $T_c$ which attains a broad maximum of 37 K at $\sim$7 GPa (this is one of the highest $T_c$ ever reported for a binary solid) before decreasing to 6 K upon further compression to $\sim$14 GPa. Complementary synchrotron X-ray diffraction at 16 K was used to measure the low-temperature isothermal compressibility of $\alpha$-FeSe, revealing an extremely soft solid with a bulk modulus, $K_0$ = 30.7(1.1) GPa and strong bonding anisotropy between inter- and intra-layer directions that transforms to the more densely packed $\beta$-polymorph above $\sim$9 GPa. The non-monotonic $T_c$($P$) behavior of FeSe coincides with drastic anomalies in the pressure evolution of the interlayer spacing, pointing to the key role of this structural feature in modulating the electronic properties.

The heavy fermion antiferromagnet CeNiGe2 was investigated under pressure by resistivity and ac calorimetry up to 4 GPa and down to 40 mK. The two magnetic transitions found in both resistivity and specific heat at 0.1 GPa at T_N1=3.95 and T_{N2}=3.21 K are replaced by a single one at 0.7 GPa and 2.81 K. Increasing pressure initially reduces this further, however at about 1.7 GPa a new transition appears, accompanied by a marked change in the pressure dependence of the ordering temperatures, the temperature dependence of the resistivity, and the residual resistivity. There are signs that this new transition has some first order character. The phase diagram of CeNiGe2 bears little resemblance to the Doniach phase diagram widely used to classify heavy fermion compounds., Comment: 4 pages, 3 figures, affiliations updated