The de Haas-van Alphen effect, exchange splitting and Curie temperature in the weak itinerant ferromagnetic Ni3Al

Ultra-high vacuum compatible preparation chain for intermetallic compounds

We report the development of a versatile material preparation chain for intermetallic compounds, which focuses on the realization of a high-purity growth environment. The preparation chain comprises an argon glovebox, an inductively heated horizontal cold boat furnace, an arc melting furnace, an inductively heated rod casting furnace, an optically heated floating-zone furnace, a resistively heated annealing furnace, and an inductively heated annealing furnace. The cold boat furnace and the arc melting furnace may be loaded from the glovebox by means of a load-lock permitting to synthesize compounds starting with air-sensitive elements while handling the constituents exclusively in an inert gas atmosphere. All furnaces are all-metal sealed, bakeable, and may be pumped to ultra-high vacuum. We find that the latter represents an important prerequisite for handling compounds with high vapor pressure under high-purity argon atmosphere. We illustrate the operational aspects of the preparation chain in terms of the single-crystal growth of the heavy-fermion compound CeNi₂Ge₂.

Quantum oscillations from nodal bilayer magnetic breakdown in the underdoped high temperature superconductor YBa2Cu3O(6+x)

We report quantum oscillations in underdoped YBa2Cu3O6.56 over a significantly large range in magnetic field extending from ≈24 to 101 T, enabling three well-spaced low frequencies at ≈440±10, 532±2, and 620±10  T to be clearly resolved. We show that a small nodal bilayer coupling that splits a nodal pocket into bonding and antibonding orbits yields a sequence of frequencies, F0-ΔF, F0, and F0+ΔF and accompanying beat pattern similar to that observed experimentally, on invoking magnetic breakdown tunneling at the nodes. The relative amplitudes of the multiple frequencies observed experimentally in quantum oscillation measurements are shown to be reproduced using a value of nodal bilayer gap quantitatively consistent with that measured in photoemission experiments in the underdoped regime.

Magnetic properties of Ni(3)Al and Ni(3)Ga: emergent states and the possible importance of a tri-critical point

We present a study of the magnetic properties of the itinerant-electron systems Ni(3)Al and Ni(3)Ga at ambient pressure. In both compounds the magnetization and susceptibility show a non-Fermi liquid form. We test these properties using a mean-field model of enhanced spin fluctuations on the border of ferromagnetism in three dimensions with no adjustable parameters. While Ni(3)Al is found to be explained well by the standard form of such a model, the data on Ni(3)Ga require us to extend the model to take into account the fact that this system lies close to a tri-critical point. We suggest that such a quantum tri-critical point may be a key feature in the understanding of quantum critical systems more generally.