Publications by Bastien Dalla Piazza

Staggered flux state for rectangular-lattice spin-1/2 Heisenberg antiferromagnets

Dmitri Ivanov, Bastien Dalla Piazza, Henrik Moodysson Rønnow, Noore Elahi Shaik

We investigate the spin-1/2 Heisenberg model on a rectangular lattice, using the Gutzwiller projected variational wave function known as the staggered flux state. Using Monte Carlo techniques, the variational parameters and instantaneous spin-spin correlat ...

AMER PHYSICAL SOC2020

Phase diagram of diluted Ising ferromagnet LiHoxY1-xF4

Conradin Kraemer, Bastien Dalla Piazza, Julian Piatek, Henrik Moodysson Rønnow, Neda Nikseresht Ghanepour, Ivan Kovacevic, Peter Babkevich

We present a systematic study of the phase diagram of LiHoxY1-xF4 (0.25

Amer Physical Soc2016

Fractional excitations in the square-lattice quantum antiferromagnet

Dmitri Ivanov, Bastien Dalla Piazza, Martin Mourigal, Henrik Moodysson Rønnow, Goran Nilsen, Mechthild Enderle

Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 par ...

Nature Publishing Group2015

Crystal Structure, Transport, and Magnetic Properties of an Ir6+ Compound Ba8Al2IrO14

László Forró, Arnaud Magrez, Alla Arakcheeva, Bastien Dalla Piazza, Ana Akrap, Krunoslav Prsa, Henrik Moodysson Rønnow, Jacim Jacimovic, Sergiy Katrych, Andrea Pisoni, Lin Yang

The novel iridate Ba8Al2IrO14 was prepared as single crystals by self-flux method, thereby providing a rare example of an all-Ir(VI) compound that can be synthesized under ambient pressure conditions. The preparation of all-Ir6+ iridate without using tradi ...

2015

Magnons in tetragonal CuO

Marco Grioni, Frédéric Mila, Bastien Dalla Piazza, Henrik Moodysson Rønnow, Simon Karl Moser, Sara Fatale, Noore Elahi Shaik, Thorsten Schmitt

We investigate by resonant inelastic x-ray scattering the magnetic excitations in thin films of tetragonal CuO. We identify a spin wave excitation, dispersing on two cupratelike antiferromagnetic sublattices. Its energy at the boundary of the Brillouin zon ...

2015

Neutron spectroscopic study of crystal-field excitations and the effect of the crystal field on dipolar magnetism in LiRF4 (R = Gd, Ho, Er, Tm, and Yb)

Conradin Kraemer, Bastien Dalla Piazza, Henrik Moodysson Rønnow, Ivan Kovacevic, Peter Babkevich

We present a systematic study of the crystal-field interactions in the LiRF4 (R = Gd, Ho, Er, Tm, and Yb) family of rare-earth magnets. Using detailed inelastic neutron scattering measurements, we have been able to quantify the transition energies and wave ...

American Physical Society2015

Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates

Helmuth Berger, Marco Grioni, Bastien Dalla Piazza, Henrik Moodysson Rønnow, Marco Guarise, Thorsten Schmitt

The high-T-c cuprate superconductors are close to antiferromagnetic order. Recent measurements of magnetic excitations have reported an intriguing similarity to the spin wavesmagnons- of the antiferromagnetic insulating parent compounds, suggesting that ma ...

Nature Publishing Group2014

Theories of Experimentally Observed Excitation Spectra of Square Lattice Antiferromagnets

Bastien Dalla Piazza

The first part of this thesis presents the theoretical study of an anomaly of unknown origin in the excitation spectrum of the Quantumspin-1/2 Heisenberg Square lattice Anti-Ferromagnet. The anomaly manifests itself in Inelastic Neutron Scattering data for ...

EPFL2014

Nonequilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar-coupled spin-glass LiHo0.5Er0.5F4

Bastien Dalla Piazza, Julian Piatek, Stephen Paul Neithardt, Henrik Moodysson Rønnow, Ivan Kovacevic, Peter Babkevich

We present a study of the model spin-glass LiHo0.5Er0.5F4 using simultaneous ac susceptibility, magnetization, and magnetocaloric effect measurements along with small angle neutron scattering ( SANS) at sub-Kelvin temperatures. All measured bulk quantities ...

American Physical Society2014

Quantum and thermal ionic motion, oxygen isotope effect, and superexchange distribution in La2CuO4

Sandrine Gerber, Bastien Dalla Piazza, Bruce Normand, Henrik Moodysson Rønnow, Kazimierz Conder, Vera Irina Schnells

We study the zero-point and thermal ionic motion in La2CuO4 by means of high-resolution neutron-diffraction experiments. Our results demonstrate anisotropic motion of O and, to a lesser extent, Cu ions, both consistent with the structure of coupled CuO6 oc ...

2014

Phase diagram with an enhanced spin-glass region of the mixed Ising–XY magnet LiHoxEr1-xF4

Bastien Dalla Piazza, Julian Piatek, Henrik Moodysson Rønnow, Ivica Zivkovic, Neda Nikseresht Ghanepour, Nikolay Tsyrulin

We present the experimental phase diagram of LiHoxEr1-xF4, a dilution series of dipolar-coupled model magnets. The phase diagram was determined using a combination of ac susceptibility and neutron scattering. Three unique phases in addition to the Ising fe ...

Amer Physical Soc2013

Unified one-band Hubbard model for magnetic and electronic spectra of the parent compounds of cuprate superconductors

Helmuth Berger, Marco Grioni, Bastien Dalla Piazza, Martin Mourigal, Henrik Moodysson Rønnow, Marco Guarise, Thorsten Schmitt

Using low-energy projection of the one-band t-t′-t′′ Hubbard model we derive an effective spin Hamiltonian and its spin-wave expansion to order 1/S. We fit the spin-wave dispersion of several parent compounds to the high-temperature superconducting cuprate ...

American Physical Society2012

Dipolar Antiferromagnetism and Quantum Criticality in LiErF4

Conradin Kraemer, Bastien Dalla Piazza, Julian Piatek, Henrik Moodysson Rønnow, Neda Nikseresht Ghanepour, Nikolay Tsyrulin, Gabriel Aeppli

Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF4, establishing it as a model dipolar-coupled antiferromagnet with pla ...

American Association for the Advancement of Science2012

Measurement of Magnetic Excitations in the Two-Dimensional Antiferromagnetic Sr2CuO2Cl2 Insulator Using Resonant X-Ray Scattering: Evidence for Extended Interactions

Helmuth Berger, Marco Grioni, Bastien Dalla Piazza, Ping-Hui Lin, Peng Xu, Henrik Moodysson Rønnow, Marco Guarise, Thorsten Schmitt, Dirk Van der Marel

We measured the momentum dependence of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr2CuO2Cl2 (SCOC). We identify a single-spin-wave feature and a multimagnon continuum, with different polarization dependences. The spin waves ...

American Physical Society2010