FORMATION ENTHALPY OF MONOVACANCIES IN NEUTRON-STAR MATTER
FORMATION ENTHALPY OF MONOVACANCIES IN NEUTRON-STAR MATTER
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中子星物质中单空位的形成焓
DOI：
10.1046/j.1365-8711.1999.02508.x
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发表时间：
1999
影响因子：
4.8
通讯作者：
P. B. Jones
中科院分区：
文献类型：
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作者：
P. B. Jones
对中子星物质固相中单空位形成焓的分析表明，连续中子超流体和核性质的变化都不重要。它的计算是一个涉及库仑和电子能量的明确定义的问题。获得的单空位的热平衡浓度太小，无法提供解释在船帆脉冲星中观察到的大故障序列所需的超流体-中子-涡旋钉扎强度，但单空位±涡旋相互作用，如果有吸引力，可能有助于故障后观察到的自旋下降速率的恢复。关键词：恒星：中子±脉冲星：一般。 1 引言 脉冲星故障观测给出了作为时间函数的旋转角速度和自旋下降速率的测量结果，表明中子超流体和恒星带电成分之间的耦合是复杂的。根据 Anderson & Itoh (1975) 和 Ruderman (1976) 的早期工作，人们通常认为故障是超流体中子涡旋从形成恒星固体外壳的核库仑晶格中突然大规模脱离的结果。每单位涡流长度的最大钉扎力的估计取决于涡流±核相互作用以及晶格的缺陷结构。涡旋与多晶结构的相互作用之前已被考虑过（Jones 1998a），并且表明并不能提供足够强的钉扎来解释在 Vela 脉冲星中观察到的大毛刺。从质量上讲，其原因在于无缺陷单晶的结构规律性允许涡旋在马格努斯力的作用下位移到一系列连续的新位置，而能量变化不超过极小。显着的钉扎只能由与晶格缺陷的相互作用产生。预计缺陷结构与电子II型超导体的缺陷结构有很大不同。内部冷却速率慢意味着缺陷是在局部热力学平衡下形成的，并且是那些具有低形成自由能的缺陷。电子II型超导体具有大范围的复杂缺陷，通常在制造过程中形成。单空位对晶格的干扰比间隙原子少，具有较低的形成自由能，并且预计将成为中子星物质固相中最重要的一类缺陷（Jones 1998a）。考虑到类似的第一原理自由能计算，例如在体心立方（bcc）锂的情况下，计算中子星物质中的单空位形成焓可能被认为过于雄心勃勃（参见Benedek等人，1992年；Frank等人，1993年，1996年）。然而，中子星物质中的库仑相互作用具有非常小的电子屏蔽波数，并且比锂中的原子间力简单得多。尽管在计算单空位形成焓时不能忽略电子屏蔽，但可以通过其小波数形式令人满意地近似纵向静态介电常数（Jacovici 1962），eq 1 k=q，对于波数 q p kF0 有效，其中
Analysis of the monovacancy formation enthalpy in the solid phase of neutron-star matter has shown that neither the continuous neutron super ̄uid nor changes in nuclear properties are of signi®cance. Its calculation is a well-de®ned problem involving Coulomb and electron energies. The thermal equilibrium concentrations of monovacancies obtained are too small to give super ̄uid-neutron-vortex pinning of the strength required to explain the sequence of large glitches observed in the Vela pulsar, but the monovacancy±vortex interaction, if attractive, could contribute to the recovery of the spin-down rate observed after a glitch. Key words: stars: neutron ± pulsars: general. 1 I N T R O D U C T I O N Pulsar-glitch observations, giving measurements of the rotation angular velocity and spin-down rate as functions of time, show that the coupling between the neutron super ̄uid and the electrically charged components of the star is complex. Following early work by Anderson & Itoh (1975) and Ruderman (1976), it has usually been assumed that glitches are a consequence of sudden large-scale unpinning of super ̄uid neutron vortices from the Coulomb lattice of nuclei forming the solid outer shell of the star. Estimates of the maximum pinning force per unit length of vortex depend on the vortex±nucleus interaction and on the defect structure of the lattice. Vortex interaction with a polycrystalline structure has been considered previously (Jones 1998a) and shown not to provide pinning strong enough to explain the large glitches observed in the Vela pulsar. The reason for this, qualitatively, is that the structural regularity of a defect-free single crystal allows displacement of a vortex, under a Magnus force, to a continuous sequence of new positions with no more than extremely small changes in energy. Signi®cant pinning can arise only from interaction with lattice defects. The defect structure is expected to be very different from that of electronic type II superconductors. The slow rate of internal cooling means that defects are formed in local thermodynamic equilibrium and are those with low free energy of formation. Electronic type II superconductors have large-scale complex defects, usually formed in the fabrication process. Monovacancies disturb a lattice less than interstitials, have lower free energy of formation, and are expected to be the most important class of defect in the solid phase of neutron-star matter (Jones 1998a). Calculation of monovacancy formation enthalpy in neutron-star matter might be considered overambitious given that the analogous ®rst-principles free energy calculations, for example, in the case of body-centred cubic (bcc) lithium are a ®eld of current activity in condensedmatter physics (see Benedek et al. 1992; Frank et al. 1993, 1996). However, the Coulomb interaction in neutron-star matter has a very small electron screening wavenumber and is much simpler than the interatomic force in lithium. Although electron screening cannot be neglected in a calculation of monovacancy formation enthalpy, it is possible to approximate the longitudinal static dielectric constant (Jancovici 1962) satisfactorily by its small wavenumber form, e
q 1 k=q, valid for wavenumbers q p kF0, where