They analyze the role of the delicate interplay of Eu magnetism, strain, and pressure on the realization of nontrivial topological phases. For that they invoke a combination of a group theoretical analysis with ab initio density functional theory calculations and uncover a rich phase diagram with various nontrivial topological phases beyond a Weyl semimetallic state, such as axion and topological crystalline insulating phases, and discuss their realization.
09.11.2023 Libor Šmejkal wins the "Falling Walls Science Breakthrough of the Year 2023" award in physical sciences
Congratulations to Libor Šmejkal for winning the Falling Walls Science Breakthrough of the Year 2023 award in physical sciences.
In the Falling Walls science summit the brightest minds in science, politics, business and the media come together to present groundbreaking discoveries and scientific breakthroughs and emerging trends that shape our world. Libor was awarded for his his breakthrough of altermagnets—a discovery that has the potential to revolutionise the way we design and use electronic technology, making it much more efficient and sustainable.
They examine the spin-transfer and topological Hall physics of metallic frustrated magnets and show that SO(3) solitons and magnetic disclinations mediate previously unidentified contributions to the corresponding effects, with no analog in collinear magnetism. In particular, they present a minimal low-energy long-wavelength theory of the Yang-Mills type for the itinerant carriers and also discuss the emergent electrodynamics mediated by the topological solitons/defects arising in the noncoplanar magnetic background. They also considered the effect of symmetry reduction (with respect to the case of full rotational symmetry) on both spin-transfer and topological Hall responses of the magnetic conductor. Furthermore, they discuss experimental setups for the detection of the aforesaid Hall currents. Their findings open new avenues for the detection of topological solitons/defects in magnetic systems with order-parameter manifolds beyond the conventional S2 paradigm.
They used a field-induced reorientation of the Néel vector from the easy-axis toward the  hard-axis to demonstrate the anomalous Hall signal in this RuO2. They confirm the existence of an anomalous Hall effect in our RuO2 thin-film samples, whose set of magnetic and magneto-transport characteristics is consistent with the earlier report. By performing their measurements at extreme magnetic fields up to 68 T, they reach saturation of the anomalous Hall signal at a field Hc ≃ 55 T that was inaccessible in earlier studies but is consistent with the expected Néel-vector reorientation field.
They excite Mn2Au thin films with phase-locked single-cycle terahertz electromagnetic pulses and monitor the spin response with femtosecond magneto-optic probes. They observe signals whose symmetry, dynamics, terahertz-field scaling and dependence on sample structure are fully consistent with a uniform in-plane antiferromagnetic magnon driven by field-like terahertz NSOTs with a torkance of (150 ± 50) cm2 A−1 s−1. Their research indicates that fully coherent Néel-vector switching by 90° within 1 ps is within close reach.
A joint publication with Tobias Wagner and Helen Gomonay about coupling of ferromagnetic and antiferromagnetic spin dynamics in Mn2Au/NiFe thin film bilayers has been published in Physical Review Letters.
They investigate magnetization dynamics of Mn2Au/Py (Ni80Fe20) thin film bilayers using broadband ferromagnetic resonance (FMR) and Brillouin light scattering spectroscopy. Their model reveals the dependence of the hybrid modes on the AFMR frequencies and interfacial coupling as well as the evanescent character of the spin waves that extend across the Mn2Au/Py interface.
The workshop focusses on correlated states of electrons, that give rise to quantum matter, such as ordered magnets, spin liquids, superconductors, and topological materials. The exciting phenomena hosted and technological applications promised by these states of matter have further inspired the scientific community to engineer hybrids where different ingredients for correlations are provided by separate materials coupled together. Thus, such low-dimensional hybrid nanostructures have enabled engineering novel states of matter with intriguing physics, often not admitted by any single platform.
With the recent developments, theoretical and experimental, time reversal symmetry breaking via magnetism has emerged as a powerful tool to engineer novel unconventional superconducting states and phenomena such as nonreciprocity. At the same time, engineering of the superconducting condensate to bear a net spin employing magnet/superconductor hybrids has been demonstrated. This has opened prospects for superconducting spintronics devices enabling dissipationless spin torques and logic. Further, spin fluctuations appear to play a fundamental role in a large fraction of unconventional and two-dimensional superconductors including the recently discovered states in moiré materials. Therefore, these three seemingly disjoint fields are intricately relying on knowledge from each other and can best be tackled with an overview of all three. Providing this overview and a common discussion platform is the main goal of this workshop.
The workshop shall bring together experts and young researchers from three different communities: (i) Magnetism and Spintronics, (ii) Superconductivity and Strongly Correlated Electrons, and (iii) Low-dimensional nanostructures. The purview includes coherent and incoherent magnetization dynamics in conjunction with the various spintronics effects that allow its manipulation and detection. A key topic will be the recently discovered nonreciprocal effects in magnets e.g., chiral magnons, as well as superconductors, e.g., the superconducting diode effect. Recent discoveries regarding two-dimensional materials, multi-orbital superconductivity, Ising superconductors, topological superconductivity and quantum sensors coupled to magnets will also be central to the workshop portfolio. Employing fluctuations of currents (e.g, flow of spin or vortices) to probe the quantum nature of transport will form an exciting topic of discussion across communities. Finally, the case of spin fluctuations mediated superconductivity, that is believed to underlie a wide range of unconventional superconductors can best be discussed with the three communities present at the workshop.
They reveal the emergence of large photocurrents of spin in collinear Mn2Au, whose properties can be understood as a result of a non-linear optical version of the spin Hall effect, which they refer to as the photospin Hall effect, encoded into the relation between the driving charge and resulting spin photocurrents. Moreover, they suggest that even a very small canting in Mn2Au can give rise to colossal spin photocurrents that are chiral in flavor. They conclude that the combination of staggered magnetization with the structural and electronic properties of this material results in a unique blend of prominent
photocurrents, which makes Mn2Au a unique platform for advanced optospintronics applications.
You can find the publication under APL Mater 11, 071106.
The workshop focusses on THz spintronics, which is a novel research field that combines magnetism and spintronic with ultrafast optics. Although ultrafast demagnetization of ferromagnetic materials at picosecond timescale has been first observed already three decades ago, recent years have seen the rapid development of THz spintronic devices stemming from ground breaking studies. In the last years, the numerous improvements made in material research (such as on topological insulators and antiferromagnetic materials), interface quality and device engineering have been central to both explore spin-based physics at THz frequencies and investigate to new concepts of spin based THz devices. These cover the full THz block chain (broad and narrowband THz generation and detection, together with control of radiation properties such as polarization and ellipticity) as well as new approaches for THz imaging and encoding THz information. This workshop will bring together world-leading scientists from a broad range of communities, generating further collaborations and developmentsin this emerging field.
You can apply online for the workshop until August 14th, 2023.