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• In 8- Pmmn borophene, the real-space propagation of Dirac fermions is unique. • The anisotropic behaviors of RKKY interaction is velocity-determined. • The measurement of RKKY interaction can be used to identify band features. • The tunable RKKY interaction of 8- Pmmn borophene is useful in spin fields. As a new two-dimensional Dirac material, 8- Pmmn borophene hosts novel anisotropic and tilted massless Dirac fermions (MDFs) and has attracted increasing interest. However, the potential application of 8- Pmmn borophene in spin fields has not been explored. Here, we study the long-range RKKY interaction mediated by anisotropic and tilted MDFs in magnetically-doped 8- Pmmn borophene. To this aim, we carefully analyze the unique real-space propagation of anisotropic and tilted MDFs with noncolinear momenta and group velocities. As a result, we analytically demonstrate the anisotropic behaviors of long-range RKKY interaction, which have no dependence on the Fermi level but are velocity-determined, i.e., the anisotropy degrees of oscillation period and envelop amplitude are determined by the anisotropic and tilted velocities. The velocity-determined RKKY interaction favors to fully determine the characteristic velocities of anisotropic and tilted MDFs through its measurement, and has high tunability by engineering velocities shedding light on the application of 8- Pmmn borophene in spin fields. [ABSTRACT FROM AUTHOR]

Recently, the altermagnetic materials with spin splitting effect (SSE), have drawn significant attention due to their potential to the flexible control of the spin polarization by the Néel vector. Here, the direct and inverse altermagnetic SSE (ASSE) in the (101)‐oriented RuO2 film with the tilted Néel vector are reported. First, the spin torque along the x‐, y‐, and z‐axis is detected from the spin torque‐induced ferromagnetic resonance (ST‐FMR), and the z‐spin torque emerges when the electric current is along the [010] direction, showing the anisotropic spin splitting of RuO2. Further, the current‐induced modulation of damping is used to quantify the damping‐like torque efficiency (ξDL) in RuO2/Py, and an anisotropic ξDL is obtained and maximized for the current along the [010] direction, which increases with the reduction of the temperature, indicating the present of ASSE. Next, by way of spin pumping measurement, the inverse altermagnetic spin splitting effect (IASSE) is studied, which also shows a crystal direction‐dependent anisotropic behavior and temperature‐dependent behavior. This work gives a comprehensive study of the direct and inverse ASSE effects in the altermagnetic RuO2, inspiring future altermagnetic materials and devices with flexible control of spin polarization. [ABSTRACT FROM AUTHOR]

We report the experimental evidence of evolving lattice distortion in high quality epitaxial orthorhombic SrIrO3(001) thin films fully strained on (001) SrTiO3 substrates. Angle-resolved X-ray photoemission spectroscopy studies show that the surface layer of 5 nm SrIrO3 films is Sr–O terminated, and subsequent layers recover the semimetallic state, with the band structure consistent with an orthorhombic SrIrO3(001) having the lattice constant of the substrate. While there is no band folding in the experimental band structure, additional super-periodicity is evident in low energy electron diffraction measurements, suggesting the emergence of a transition layer with crystal symmetry evolving from the SrTiO3 substrate to the SrIrO3(001) surface. Our study sheds light on the misfit relaxation mechanism in epitaxial SrIrO3 thin films in the orthorhombic phase, which is metastable in bulk. [ABSTRACT FROM AUTHOR]

Motivated by the experimental huge enhancement of the superconducting transition temperature $$T_\mathrm{c}$$ in FeSe superconductor under high pressure, we perform first-principles calculations of the evolutions of structural, electronic, and lattice dynamical properties of FeSe at varying hydrostatic pressures up to 8 GPa. The pressure response is anisotropic with a larger compressibility along $$c$$ -axis. At ambient pressure, Fermi surface nesting between hole and electron pockets induces spin density wave (SDW) order at the vector ( $$\pi $$ , $$\pi $$ , 0) with a collinear antiferromagnetic structure. With the increase of pressure, the Fermi surface nesting is reduced, and therefore the SDW is suppressed, which could not enhance superconductivity based on the spin-fluctuation scenario. For the phonon dispersion, the bands have blue-shift except for the modes around 100 cm $$^{-1}$$ , indicating hardening of the vibration modes in a wide frequency range. Furthermore, the electron-phonon coupling constant and the corresponding $$T_\mathrm{c}$$ by McMillan equation are calculated. However, there is no obvious enhancement of $$T_\mathrm{c}$$ under pressure, which further rules out the conventional phonon-mediated superconductivity of FeSe. Maybe the local magnetic moment plays an important role for the superconductivity and enhancement of $$T_\mathrm{c}$$ under pressure. [ABSTRACT FROM AUTHOR]