J. Larrea

TU Wien

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E. Baggio‐Saitovitch

Centro Brasileiro de Pesquisas Físicas

S. Paschen

TU Wien

Valentina Martelli

Universidade de São Paulo

H. M. Rønnow

École Polytechnique Fédérale de Lausanne

F. J. Litterst

Technische Universität Braunschweig

D. R. Sánchez

Universidade Federal Fluminense

A. Prokofiev

TU Wien

J. Haenel

TU Wien

A. M. Strydom

University of Johannesburg

F. J. Litterst

Technische Universität Braunschweig

Cooperative Institutions

Centro Brasileiro de Pesquisas Físicas

TU Wien

Paul Scherrer Institute

Columbia University

École Polytechnique Fédérale de Lausanne

Rice University

McMaster University

Universidade Federal do Rio de Janeiro

ETH Zurich

Technical University of Munich

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Sequential localization and strange-metal behavior of a complex electron fluid

Valentina Martelli A. Cai Emilian M. Nica Mathieu Taupin A. V. Prokofiev

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Phase separation and suppression of critical dynamics at quantum phase transitions of MnSi and (Sr1−xCax)RuO3

Nature Physics (2006)

Y. J. Uemura T. Goko I. M. Gat-Malureanu J. P. Carlo Peter L. Russo

Magnetism

10.1038/nphys488

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Citations (157)

A quantum magnetic analogue to the critical point of water

Research Square (Research Square) (2020)

H. M. Rønnow J. Larrea S. P. G. Crone Ellen Fogh Mohamed Zayed

Abstract At the familiar liquid-gas phase transition in water, the density jumps discontinuously at atmospheric pressure, but the line of these first-order transitions defined by increasing pressures terminates at the critical point [1], a concept ubiquitous in statistical thermodynamics [2]. In correlated quantum materials, a critical point was predicted [3] and measured [4, 5] terminating the line of Mott metal-insulator transitions, which are also first-order with a discontinuous charge density. In quantum spin systems, continuous quantum phase transitions (QPTs) [6] have been investigated extensively [7-11], but discontinuous QPTs have received less attention. The frustrated quantum antiferromagnet SrCu2(BO3)2 constitutes a near-exact realization of the paradigmatic Shastry-Sutherland model [12-14] and displays exotic phenomena including magnetization plateaux [15], anomalous thermodynamics [16] and discontinuous QPTs [17]. We demonstrate by high-precision specific-heat measurements under pressure and applied magnetic field that, like water, the pressure-temperature phase diagram of SrCu2(BO3)2 has an Ising critical point terminating a first-order transition line, which separates phases with different densities of magnetic particles (triplets). We achieve a quantitative explanation of our data by detailed numerical calculations using newly-developed finite temperature tensor-network methods [16, 18-20]. These results open a new dimension in understanding the thermodynamics of quantum magnetic materials, where the anisotropic spin interactions producing topological properties [21, 22] for spintronic applications drive an increasing focus on first-order QPTs.

Critical point (mathematics)

10.21203/rs.3.rs-85772/v1

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Sequential localization of a complex electron fluid

Proceedings of the National Academy of Sciences (2019)

Valentina Martelli Ang Cai Emilian M. Nica Mathieu Taupin A. Prokofiev

Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with 2 distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin-orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.

10.1073/pnas.1908101116

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Magnetic order of intermetallicFeGa3−yGeystudied byμSRand

Physical review. B./Physical review. B (2017)

J. Munévar M. Cabrera-Baez M. Alzamora J. Larrea E. M. Bittar

Temperature-dependent magnetization, muon spin rotation, and $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy experiments performed on crystals of intermetallic ${\mathrm{FeGa}}_{3\ensuremath{-}y}{\mathrm{Ge}}_{y}$ $(y=0.11,0.14,0.17,0.22,0.27,0.29,0.32)$ are reported. Whereas at $y=0.11$ even a sensitive magnetic microprobe such as $\ensuremath{\mu}\mathrm{SR}$ does not detect magnetism, all other samples display weak ferromagnetism with a magnetic moment of up to $0.22{\ensuremath{\mu}}_{B}$ per Fe atom. As a function of doping and of temperature, a crossover from short-range to long-range magnetic order is observed, characterized by a broadly distributed spontaneous internal field. However, $y=0.14$ and 0.17 remain in the short-range-ordered state down to the lowest investigated temperature. The transition from short-range to long-range order appears to be accompanied by a change of the character of the spin fluctuations, which exhibit a spin-wave excitation signature in the long-range-order part of the phase diagram. M\"ossbauer spectroscopy for $y=0.27$ and 0.32 indicates that the internal field lies in the plane perpendicular to the crystallographic $c$ axis. The field distribution and its evolution with doping suggest that the details of the Fe magnetic moment formation and the consequent magnetic state are determined not only by the dopant concentration, but also by the way the replacement of the Ga atoms surrounding the Fe is accomplished.

Muon spin spectroscopy

Magnetism

10.1103/physrevb.95.125138

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Charge delocalization in the ludwigite Fe₃O₂BO₃

Journal of Physics Condensed Matter (2001)

J. Larrea D. R. Sánchez F. J. Litterst E. Baggio‐Saitovitch

57Fe Mössbauer spectra of Fe3O2BO3 reveal a combined effect of charge ordering and electron delocalization between 112 and 450 K. On the basis of the temperature dependence of the isomer shifts and quadrupole interactions, together with the information from previously obtained transport data, we are able to discuss the arrangement of Fe2+ and Fe3+ in the structure and the dynamics of the electronic configurations. We found a charge-delocalization transition around 300 K. Below this temperature, formation of pairs of Fe ions with mixed valence takes place in part of the crystalline structure.

Charge ordering

10.1088/0953-8984/13/48/105

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Quantum criticality of the heavy-fermion compound CeCoGe{sub 2.2}Si{sub 0.8}

J. Larrea S. Paschen A. Sidorenko M. Müller Valentina Martelli

Full text: The pressure-tuned quantum critical point (QCP) of the antiferromagnetic heavy-fermion compound CeCoGe{sub 2.1}Si{sub 0.9} was claimed to be dominated by the coexistence of both spin fluctuations and disorder. We will present electrical resistivity, magnetic susceptibility and specific heat measurements up to 15 kbar and down to 0.05 K, and establish the pressure−temperature phase diagram for CeCoGe{sub 2.2}Si{sub 0.8}. The critical behavior shall be compared to the one observed for both CeCoGe{sub 2.1}Si{sub 0.9} and the pure reference compound CeCoGe{sub 3}. We expect this investigation to elucidate the role of disorder. (author)

Specific heat

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Magnon excitations and quantum critical behavior of the ferromagnet U4Ru7Ge6

Physical review. B./Physical review. B (2018)

Mylena Nascimento M. A. Contínentino A. López Ana de Leo D. C. Freitas

We present an extensive study of the ferromagnetic heavy-fermion compound ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$. Measurements of electrical resistivity, specific heat, and magnetic properties show that ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$ orders ferromagnetically at ambient pressure with a Curie temperature ${T}_{C}=6.8\ifmmode\pm\else\textpm\fi{}0.3$ K. The low-temperature magnetic behavior of this soft ferromagnet is dominated by the excitation of gapless spin-wave modes. Our results on the transport properties of ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$ under pressures up to 2.49 GPa suggest that ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$ has a putative ferromagnetic quantum critical point (QCP) at ${P}_{c}\ensuremath{\approx}1.7\ifmmode\pm\else\textpm\fi{}0.02$ GPa. In the ordered phase, ferromagnetic magnons scatter the conduction electrons and give rise to a well-defined power law temperature dependence in the resistivity. The coefficient of this term is related to the spin-wave stiffness, and measurements of the very low temperature resistivity show the behavior of this quantity as the ferromagnetic QCP is approached. We find that the spin-wave stiffness decreases with increasing pressure, implying that the transition to the nonmagnetic Fermi liquid state is driven by the softening of the magnons. The observed quantum critical behavior of the magnetic stiffness is consistent with the influence of disorder in our system. At quantum criticality ($P={P}_{c}\ensuremath{\approx}1.7\ifmmode\pm\else\textpm\fi{}0.02$ GPa), the resistivity shows the behavior expected for an itinerant metallic system near a ferromagnetic QCP.

Magnon

10.1103/physrevb.98.174431

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Anisotropic Thermopower of the Kondo Insulator CeRu4Sn6 (vol 43, pg 2440, 2014)

J. Haenel H. Winkler M. Ikeda J. Larrea J. V. Martelli

Kondo insulator

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Evidence for Kondo effect in Zn:Fe

Bulletin of the American Physical Society (2006)

E. Baggio‐Saitovitch P. Munayco J. Larrea Y.T. Xing H. Micklitz

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